The Cavaliers called time out after rookie Michael Carter-Williams' 3-pointer over Irving tied the game with 11.3 seconds remaining. Irving, who missed potential game-winning shots at the end of regulation and the first overtime, took the inbounds pass, avoided a double team near the top of the key, drove the lane and scored on a left-handed lay-in.
Philadelphia called time out, but Carter-Williams' inbounds pass went out of bounds.
Thaddeus Young's lay-in with 5.5 seconds remaining tied the game in regulation and Evan Turner's baseline drive tied it with 8.7 seconds left in the first overtime.
Dion Waiters scored 24 points and Jarret Jack added 20 for the Cavaliers in the second game of the home-and-home set.
Turner led the Sixers with 31 points and Young had 29.
Irving scored 13 points in the final period to help Cleveland overcome a 10-point deficit. He hit a 3-pointer and a jumper and Jack added a 3-pointer from the corner to make it 87-86. Irving's three-point play gave Cleveland a 93-92 lead with 6:56 remaining. Cleveland stretched the lead to 97-92, but Turner's two free throws made it 104-103 with 1:04 to go.
Jack's jumper from the corner with 45.7 seconds remaining pushed the lead to three points, but Spencer Hawes' basket with 32.4 seconds left made it 106-105. Jack missed from the corner, but Tristan Thompson grabbed the rebound and split two free throws with 10.5 seconds to go. Young tied the game with a strong drive past Thompson.
Cleveland built a 116-109 lead with 1:35 left in the first OT, but the Sixers rallied again.
Philadelphia, picked by many to be one of the worst teams in the league, has been an early season surprise. The Sixers won their first three games, including victories over Miami and Chicago, but then had home losses to Golden State and Washington by a total of 34 points. The Sixers rallied from a 14-point deficit in the first quarter Friday to blow out the Cavaliers and picked up that momentum in the second half Saturday.
Cleveland center Andrew Bynum didn't play in order to rest his sore knees. The 7-footer has yet to play in games on back-to-back nights as he works his way back from surgery on both knees. Bynum was booed throughout his return to Philadelphia on Friday when he scored four points and had five rebounds in 18 minutes.
Cavaliers rookie forward Anthony Bennett, who strained his right shoulder Friday, was scoreless in nine minutes. Bennett, the No. 1 pick in the NBA draft, has struggled in the early going of his first season, hitting 1 of 21 shots from the field.
NOTES: Irving, who is listed at 6-foot-3 and 193 pounds, took a charge from Sixers C Hawes, who is 7-1 and 245 pounds, in the second quarter. ... Alonzo Gee started at small forward for Cleveland in place of Earl Clark, who started the first six games, but is averaging four points and shooting 30 percent from the field. Gee scored two points in 22 minutes while Clark didn't play. ... C Daniel Orton (sore right knee) missed his second straight game for the Sixers. He was injured Wednesday against the Wizards.