The Celtics remain in the playoff spots, and now have a record of 37-23.
Saturday night’s game was disappointing after they allowed Zach LaVine and Lauri Markkanen to dominate with a combined 77 points.
The Bulls had a record of 15-44 going into the game and the Celtics were the overwhelming favourites to come out on top.
The Celtics have been disappointing this season when compared with their pre-season expectations.
Many pundits believed Boston would challenge for the NBA title and anything less than a trip to the finals would be classed as a failure.
Irving scored 37 points with 10 assists and five rebounds in the loss.
But afterwards, he insisted he was still confident of his team’s chances in the postseason.
“I don’t get frustrated anymore,” Irving said.
“This is all part of our season.
“It’ll be fine. Why? Because I’m here.
“As a team, as a collective we all have winning at the forefront of our mind, at least I hope so.
“You just have to adapt. The teams that adapt the quickest, or adapt at the right time are successful in the playoffs.
“We’re still waiting for that thing to click.
“We have gone on eight-game, six-game, four-game winning streaks, then we hit a lull of three games and we’re back answering questions like this.”
The Celtics are next in action on Tuesday night as they face a crunch game against the Toronto Raptors.