Five takeaways from Celtics' preseason

Marcus Smart and Jared Sullinger are two keys to the Celtics' fortunes this season. Mark L. Baer/USA TODAY Sports

The Boston Celtics posted a 6-1 record during preseason play and, while you can make the case that they didn't play the most daunting competition -- two games against European squads and a five-game slate with Atlantic Division foes that culminated with a nearly unwatchable win over the Philadelphia 76ers on Friday night -- the Celtics can pluck plenty of positives from the exhibition season.

Here are five takeaways from Boston's preseason:

1. The Celtics emerged healthy

This is no insignificant accomplishment for a team that was ravaged by illness and dealt with a bunch of minor dings over the past three weeks. For the only time in the preseason, coach Brad Stevens was able to say, "Everybody's available" before Friday's exhibition finale and he celebrated by playing all 17 of his guys. Now the key is keeping them upright until Wednesday night when the Celtics open the 2015-16 regular season against the 76ers.

"Knock on wood, we walk out of here healthy," Stevens said Friday when asked to assess the preseason. "So that’s obviously goal No. 1, right?" Avery Bradley bruised his shin on Thursday, but played the first quarter on Friday and showed no ill-effects. Isaiah Thomas, the team's second-unit spark plug, missed two games this week with his own left shin issue and some tendinitis in his knee. He had a rough shooting night Friday, but the Celtics are hoping he was just shaking off any rust that had gathered. Jae Crowder has battled through a sprained thumb, but it won't keep him off the floor. The Celtics should have a full roster on opening night beyond -- well beyond Kelly Olynyk, who is suspended for the first game for the shoulder-tugging incident with Kevin Love during the playoffs.

2. The Celtics have a starting lineup ... but don't get attached

Stevens appears ready to trot out a starting lineup that features Marcus Smart, Bradley, Crowder, David Lee, and Tyler Zeller. That also allow Stevens to pair Thomas with guys like Amir Johnson and Olynyk off the bench. The preseason seemed to show that those groups worked best together with the first unit able to run some offense through Lee and take pressure off second-year and still-learning point guard Smart. The Thomas/Johnson pick-and-rolls were extremely effective and shooters like Olynyk and Jonas Jerebko will benefit from the open looks they'll generate.

All that said, don't get too attached to this rotation. Stevens has repeated ad nauseum that he will use Boston's depth as a weapon and won't hesitate to mix and match personnel to give the Celtics a better chance at success. We suspect that will mean a lot of third-quarter tinkering like we saw last season when Stevens would often swap out a big to generate a more favorable matchup or ride a hot hand. While keeping players happy with their playing time is the biggest challenge for Stevens with this deep and even roster, the ability to go 12 deep and get creative with matchups is a small luxury. Twelve different players started games for Boston last season -- aided in large part by the 11 trades and 41 different roster players the Celtics carried -- but it wouldn't be a surprise to see Stevens start a similar number this year even with more roster stability.

3. The rookies are intriguing ... but most game reps will come in Maine

Part of the preseason fun is getting an extended glimpse at younger players who might not necessarily see a bunch of time during the regular season. We joked about it, but each of Boston's three rookies -- and you can add second-year guard James Young in that mix, too -- had "Hype Train" moments where fans get (overly) excited about their potential. With Stevens pledging to stick with a 10-man rotation, it's difficult to see where these younger players are going to get consistent minutes, but there will be opportunities over the course of the 82-game season and it'll be how each player embraces those chances that impacts how quickly they elevate. Regardless, Boston's young players will also spend a ton of time commuting to Maine to get extended game reps in the D-League, which are necessary for those players to continue their pro development and build their confidence.

The encouraging part is that none of Boston's three rookies -- Terry Rozier, R.J. Hunter, and Jordan Mickey -- ever looked truly out of place. Rozier displayed better-than-expected shooting, especially from beyond the 3-point arc, and a combination of speed and defensive feistiness will give him a chance to carve out Phil Pressey-like third-string minutes. Hunter showed a high basketball IQ, but made only 6 of 21 3-point attempts (28.6 percent) and must knock down shots in order to get a sustained opportunity. Mickey needs to learn how to play against NBA bigs, but his athleticism gives him an ability to compensate for the size disadvantage.

4. The #AmirEffect

The player with the best defensive rating on the team during the preseason? Isaiah Thomas with a rub-your-eyes rating of 80.8 points allowed per 100 possessions. Thomas was an adequate one-on-one defender with Synergy Sports data pegging him in the 65th percentile among all players this preseason (allowing a modest 0.743 points per play). But much of Boston's success on the defensive side of the ball can be traced to newcomer Johnson.

The folks in Toronto kept saying it when Boston made Johnson its free-agent splurge this summer: Johnson's contributions won't leap off the stat sheet, but he's going to do the little things that make a big difference. Johnson, even as he adapts to a new defensive system, constantly put himself in the right spots with nothing but hustle and IQ. He proved to be an effective rim protector just by sliding over and preventing players from getting near the rim.

An example: Jae Crowder had a monster defensive preseason, twice smothering Carmelo Anthony in head-to-head matchups. But in the first quarter of Thursday's game at TD Garden, Anthony beat Crowder off the dribble and got into the paint. Johnson, on the opposite blocks, slid over and swatted Anthony at the glass, allowing the Celtics to break out in transition the other way. Stevens' system puts a heavy emphasis on help defenders and Johnson is going to erase a lot of mistakes by perimeter players. It should come as little surprise that second-unit guys that ran with Johnson had some of the best defensive ratings of the preseason, including Olynyk (84.9) and Jerebko (85.1).

5. Numbers game

A few stats that leaped off the preseason page, with the usual caveat that it's a relatively small sample against less-than-overwhelming competition:

• Olynyk owned the best net-rating -- the difference between a players' offensive (108.1) and defensive (84.9) ratings -- on the team at a staggering plus-23.3. Remember that Olynyk led the team in plus/minus last season at plus-226 overall. Good things tend to happen when he's on the floor.

• The best offensive rating on the team (well, besides training-camp cut Levi Randolph's insane 208.3 rating after making his only shot in mere seconds of playing time)? That was Zeller at 111.1. It was almost surprising how offensively effective the first unit was -- at least because of how much the first unit struggled to generate offense last season. Zeller, not surprisingly, is an effective roll man who had some late-preseason chemistry with Smart. But defense needs to be Zeller's focus in order to maintain that starting role.

• The Celtics pace with Thomas on the court was a team-best 108.3 possessions per 48 minutes. Somewhere up-tempo craving Tommy Heinsohn smiles.

• Final thought: The Celtics really need Jared Sullinger to fight his way into a role in a crowded frontcourt. The fourth-year big man was far and away the team's best rebounder while grabbing 29.7 percent of all defensive caroms and 21.5 percent of all available rebounds while on the floor. For comparison's sake: David Lee's overall rebound rate was 17.2 percent (and nobody else was above 15 percent). Of all players that appeared in at least four games this preseason, Sullinger ranked fifth in the league overall in rebound percentage behind only Andre Drummond, John Henson, Keith Benson and Roy Hibbert.