James led the Cavaliers with 22 points, but Denver took the lead for good early in the third quarter and was up by as many as 14 midway through the fourth.
"They were the more desperate team, and that's why they walked out with a win," James said. "I felt OK, good enough to go out and help the team win, and as a group we didn't have it."
The Nuggets limped into the game having lost seven of eight and were coming off Sunday's defeat at New York in which they made one field goal in the second quarter.
Denver looked like a different team Monday, placing five players in double figures. Leading 90-84, the Nuggets scored eight straight points and went ahead 98-84 on Lawson's layup with 6:01 to play.
Nuggets coach Brian Shaw praised his team's effort.
"I told the guys before the game, we're under fire in a lot of different ways, but no matter what, we have to stick together in this room," he said. "People are attacking us from everywhere. The only way we can shut everybody up is through our actions on the floor. This was our biggest win of the year so far. It might not have been a big game for them, but it was a big game for us."
Cleveland, which hit its first 11 3-pointers Saturday against Atlanta, failed to reach 100 points for the first time in six games despite having four players score 20 or more.
While some observers thought the Cavaliers would breeze through games on a nightly basis, James has said since training camp it would take time for them to come together. Cleveland lost three of four to start the season before its winning streak.
"We've got to play with our back against the wall every game," he said. "I think we felt good about a four-game winning streak. You have a team that hasn't been playing well this year come into your building and think it's going to be a cakewalk, and that's what happens."
James told reporters an hour before the opening tip that "I've been better," but "I'm walking." He said the cold has been bothering him for a couple of days. He was 8-for-18 from the field with nine rebounds and five assists.
Cleveland's winning streak began with a 110-101 victory in Denver on Nov. 7, but this matchup was a different story. Afflalo was scoreless in 31 minutes in that game, and Lawson didn't play because of an ankle injury.
"When you play a high-profile team, you focus a little more as a group," said Afflalo, who set a season high for points. "It wasn't hard to get up for this one."
Cavaliers coach David Blatt wasn't surprised the Nuggets put together a strong performance.
"I knew going into this game that this was a dangerous game," he said. "I made that point when we walked in the locker room this morning."
Nuggets small forward Alonzo Gee played the previous four seasons with the Cavaliers before being traded to Charlotte on July 27. He also spent time with New Orleans, Houston and Sacramento in the offseason before signing with Denver. Gee is averaging 3.8 points in eight games.
James was selected the Eastern Conference player of the week for a record 46th time Monday.
"It means, first of all, that you're winning, and I'm happy to be a part of a team that wins," he said. "Any time I'm awarded that award, it's very humbling."
Blatt said: "It just speaks to the true definition of greatness, which is consistency, things that you over and over do well on a consistent basis."
Nuggets: Kenneth Faried, who went in averaging 7.9 rebounds per game, had one. ... F J.J. Hickson (right knee) was inactive. The team is holding him out of back-to-back games following reconstructive surgery on his right anterior cruciate ligament.
Cavaliers: Waiters scored 16 points in the final 15 minutes. ... The Cavaliers recalled rookie C Alex Kirk from Canton of the NBA Development League. ... Six of Cleveland's next seven games are at home.
Nuggets: Return home Wednesday to play Oklahoma City.
Cavaliers: Complete a three-game homestand Wednesday against NBA champion San Antonio. James will face the Spurs for the first time since they beat Miami in last season's Finals.
Los Angeles Lakers fall to 7th in West, find hope in Anthony Davis' big night
The Lakers' 106-101 loss to the Blazers dropped them to seventh in the West with five games to play, but Anthony Davis' 36-point night was "an encouraging sign," coach Frank Vogel said.
Denver hosts Brooklyn following Irving's 45-point game
Brooklyn Nets (43-24, third in the Eastern Conference) vs. Denver Nuggets (44-23, fourth in the Western Conference)
Los Angeles and New York meet in non-conference showdown
New York Knicks (37-30, fourth in the Eastern Conference) vs. Los Angeles Clippers (45-22, third in the Western Conference)