Irving sat out Cleveland's wins in Games 2 and 3 with tendinitis. He tested the knee during the morning shootaround and again before tip-off. The Cavs announced he would play about 30 minutes before the start.
The Cavs said Irving, who is now wearing a brace, will be monitored during the game. The Cavs have a 3-0 lead in the best-of-seven series.
In the opener, Irving scored 10 points and had six assists in 27 minutes. He only played 12 minutes in the Cavs' series-clinching win in Chicago on May 14. He tweaked his knee in that game and Matthew Dellavedova started the next games at point guard.
Irving has also been slowed by a sprained right foot sustained in the opening round against Boston.
Information from The Associated Press was used in this report.