Celtics get Thunder's Jeff Green

Just before Thursday's 3 p.m. ET trade deadline, the Boston Celtics agreed to ship center Kendrick Perkins and guard Nate Robinson to the Oklahoma City Thunder for forward Jeff Green and big man Nenad Krstic in a deal the NBA approved about five hours later.

Celtics president of basketball operations Danny Ainge said Thursday night that while he "agonized" over the "very, very difficult decision" to trade Perkins, he thought the move to get Green and Krstic made the Celtics a better team going forward.

"We think it upgrades our team, ultimately," Ainge said in an interview on Boston sports radio station WEEI. "You always have to give up something of value to get something of value in return. We feel this will help our team this year and help us in the future as well."

The Celtics also received cash and a 2012 first-round pick that was previously owned by the Los Angeles Clippers as part of the deal.

Neither team was done, though.

The Celtics also traded rookie center Semih Erden and forward Luke Harangody to the Cleveland Cavaliers for a 2013 second-round draft pick. The Cavaliers waived veteran forward Leon Powe to make roster room after also trading away Mo Williams and Jamario Moon for the Clippers' Baron Davis in a separate move.

Celtics coach Doc Rivers admitted the jury is initially out on the trades but said he felt like they will pay dividends for Boston down the road.

"The bottom line is: We'll see," Rivers said Thursday before Boston's game at Denver. "We think we did pretty well today. ... Whoever is the single best player in the trade, that's who you try to get. Whether that's Jeff Green or Perk, we don't know that. Krstic is a good piece for us as well. He spreads the floor, which I think is great for [Rajon] Rondo. Jeff Green spreads the floor, too."

"We needed to get that [small forward or power forward] swing guy," Rivers added. "One of the things I was just saying is that this gives us the ability -- like the year we won it -- at times we can go small with Green at the 4 and Kevin [Garnett] at the 5, with Paul [Pierce] and Ray [Allen] spreading the floor. We've been trying to get that lineup ever since [James] Posey left. You forget how many times we did that in the playoffs, which was every fourth quarter. We haven't been able to duplicate that and, in some ways, it's hurt Rondo."

While the Celtics were unloading big men, the Thunder acquired another one, sending Morris Peterson and D.J. White to Charlotte for center Nazr Mohammed.

Ainge had said Wednesday that Perkins would be out at least a week after spraining the medial collateral ligament in his left knee. He missed 43 games this season recovering from right knee surgery.

One consideration in making the deal for Ainge was the fact that Perkins was in the final year of his contract and it appeared the two sides weren't close to an extension. The Celtics had reportedly offered him a four-year, $22 million contract. Perkins was reportedly seeking a deal worth $30 million over that same span.

Ainge said Thursday that the Celtics had offered Perkins all they could under the current collective bargaining agreement.

"[Perkins] wasn't really interested in doing a contract extension, which I understand," Ainge told WEEI. "He wanted to test the market. Last time he didn't test the market and this time he really wanted to test the market and see what his value was."

Robinson tweeted reaction to the deal: "All I can say is wowzers -- Will miss all my Boston fans I love y'all, u guys showed me love."

It's a homecoming of sorts for Green. He was selected by the Celtics in the first round (fifth overall) in the 2007 draft. But he was traded with Wally Szczerbiak and Delonte West to the then Seattle SuperSonics for Ray Allen and Glen Davis.

The Celtics' pursuit of a slashing-type player intensified when it became apparent that Marquis Daniels might miss the rest of the season with a spinal injury. Daniels himself will be rehabbing in Sacramento. The Celtics traded him and cash considerations to the Kings on Thursday for a protected second-round pick in the 2017 draft, Kings president of basketball operations Geoff Petrie announced.

Daniels appeared in 49 games for the Celtics this season. He is averaging 5.5 points and 2.3 rebounds. He has been out since bruising his spinal cord on Feb. 6 against Orlando.

"I just want to wish Perk, Luke, Semih, and Quis and everybody who was here -- those are brothers for life," Garnett said Thursday night after Boston's 89-75 loss at Denver.

Speaking of Perkins, Garnett added: "Very tough day to play basketball, to even concentrate. Just being bluntly honest. You feel like you lost a family member today. Tough day."

The Celtics are concerned about their chemistry without Perkins.

"I hate to lose a teammate like Perkins," Pierce said. "He meant so much. People don't understand chemistry is from the bus to the plane to the locker room, so it's definitely a blow. It depends on how the other guys make the adjustment."

Pierce also said this is an example of how the ruthlessness of the NBA cuts both ways.

"It's the nature of the business," he said. "People thought LeBron James was cold for leaving Cleveland the way it is. This is an example of how it happens on the management end. You can't get mad at the players because it can happen to them unexpectedly, just like a player can go where he wants. It's just the nature of the beast."

Green is averaging 15.2 points and 5.6 rebounds this season as the third option for the Thunder behind Kevin Durant and Russell Westbrook. In his three-year career, he has averaged 14.2 points and 5.8 rebounds per game.

On his Twitter account, Durant said: "Tough day for me and my teammates ... good luck to jeff green, nenad krstic."

The deal gives the Thunder the big man that they've been looking for all season. Perkins has played in just 12 games this season, but the Thunder have felt for a while that they need a veteran big man to truly compete with the Spurs, Mavs and Lakers in the West.

The deal also gives the Thunder something for Green, who becomes a restricted free agent this summer. Green had rejected a contract extension offer from the Thunder earlier this season.

For the Celtics, they take a big risk that their big men -- who are now Shaquille O'Neal, Kevin Garnett and Krstic -- can lead them. But with Jermaine O'Neal out until April after knee surgery and Shaquille O'Neal currently out with an Achilles injury, these are interesting trades for a Celtics team trying to win a championship. Krstic is an offensive talent down low, but isn't known as a rebounder or a tough defender. He is averaging 7.6 points and 4.4 rebounds per game.

Rivers indicated that once Shaquille O'Neal is healthy enough to return to action, he will be the team's starting center and his play with the starting unit this season was a big reason Boston was able to make this deal.

"Shaq's a key component of this," Rivers said. "We need to get Shaq healthy and Shaq will be healthy. If Shaq plays great, this deal was actually really good for us. That's on Shaq. We have to get Shaq in great shape, get him ready, get him healthy. He's really going to be important for us in the playoffs."

To shore up their front line in the meantime, the Celtics signed center Chris Johnson to a 10-day contract Thursday. Johnson was averaging 16.9 points, 9.6 rebounds and 2.8 blocks in 32.7 minutes per game for the D-League's Dakota Wizards and also played briefly with the Trail Blazers earlier this season.

Green is a young talent who can play both the 3 and the 4 and could be part of a longer rebuilding strategy.

As part of his wheeling and dealing on deadline day, Ainge was also able to free up three roster spots, which he intends to fill with players bought out from contracts.

"We'll see what happens and be ready to pounce on players who will be bought out," Ainge told WEEI. "There are players out there right now that we like a little bit, we're not going to rush into anything. ... We're going to take a long hard look at all the names that get bought out here. We have some roster spots available."

Erden and Harangody are both rookies and were moved, in part, for the Celtics to open those roster spots.

Erden is averaging 4.1 points and 2.9 rebounds in 37 games and has been bothered by several injuries. He is planning to have shoulder surgery to repair a partially torn labrum in the offseason. Harangody has averaged 2.3 points and 2 rebounds in 28 games.

The draft pick going to Boston from Cleveland is the Timberwolves' 2013 second-round pick that the Cavs acquired last summer as a part of a trade for Ramon Sessions and Ryan Hollins.

Robinson is averaging 7.1 points in 17.9 minutes per game this season.

Chris Sheridan covers the NBA for ESPN.com. Chad Ford is the ESPN NBA Insider. Information from ESPN.com's Brian Windhorst and ESPNBoston.com's Chris Forsberg was used in this report.