Mobley missed the previous five games with a sprained left ankle and the Cavaliers lost four of them without their big man.
Mobley is a leading contender for Rookie of the Year and tops all first-year players with 20 double-doubles. He finished Friday with 17 points, 7 rebounds, 2 steals and 2 blocks in 34 minutes.
The game was a pivotal one, as the Nets jumped ahead of Cleveland in the Eastern Conference standings from eighth to seventh. Brooklyn will finish seventh if they beat Indiana on Sunday in their final regular-season game.
The No. 7 team hosts No. 8 on Tuesday, moving into the playoffs with a victory. The loser of the 7-8 game has a second shot at the postseason by beating the winner of the game between the Nos. 9 and 10 teams on Friday.
The Associated Press contributed to this report.