He had been sick the last two days and didn't decide to hop in the car and drive to Quicken Loans Arena until about 5:15 p.m.
"I was going to stay home," he said. "I'm not going to lie, I'm tired. I want to lie down right now."
The 6-foot-3, 193-pounder had missed practice on Thursday because of his sickness. He ended up playing a team-high 42 minutes.
He admitted he came very close to vomiting during the game.
"I was this close," he said. "I was chugging Gatorade. I held it back as long as I could."
Cavs coach Mike Brown checked with his star player to see how he was feeling.
"I thought he looked gassed a little bit in the second," he said. "I asked if he was all right. He gave me that boyish smile. Once he gave me that smile, I knew he was all right."
Adding to his woes, he took an elbow to his ribs in the fourth quarter and was doubled over in pain.
They just couldn't shake free from the last-place Bucks (5-21) the entire night.
"We just haven't been able to get over the hump," Bucks coach Larry Drew said. "I thought our guys played really hard and were very, very competitive as short-handed as we were."
Irving added six assists and a career-high four blocked shots. He made 13-of-25 shots from the field. He was 0-for-5 from the 3-point line until he got to overtime when he buried both attempts from long range.
Forward Earl Clark added 14 points. He made four of six from behind the arc.
"Earl made some big shots off the bench," Brown said. "Our bench production wasn't bad. Our bench did a solid job minus Dion."
Mayo missed two 3-point attempts in the waning seconds with a chance to tie the score.
NOTES: Cavs F Anthony Bennett (sick) didn't make the trip to Chicago after the game. ... The Bucks were playing without big men Ersan Ilyasova (ankle), Zaza Pachulia (right foot fracture) and Larry Sanders (surgery on right thumb) and wing players Gary Neal (plantar fasciitis in left foot), Carlos Delfino (surgery on right foot) and Caron Butler (sore left knee). "I have three bigs and I'm starting two of them," Bucks coach Larry Drew said. "You do the math." ... Rookie Giannis Antetokounmpo made his second start at shooting guard, while O.J. Mayo will come off the bench. ... Jack leads all Eastern Conference reserves in assists with 3.7 per game.