The singer/actor hit the stage at Chicago's United Center for his first performance of his 'Forget Tomorrow' world tour since he was busted last week for DWI in New York.

Check out the video ... Justin was standing at the mic with an acoustic guitar strapped around his body as the audience cheered.

With a smile, Justin addressed the elephant in the room ... saying, “We’ve been together through ups and downs and lefts and rights, and it’s been a tough week, but you’re here, and I’m here and nothing can change this moment right now."

He added, "I know sometimes I’m hard to love, but you keep on loving me and I love you right back, thank you so much.”

Throughout his moving speech, JT's fans wildly clapped and shouted in support while, at one point, the entertainer bowed to them.

As we reported ... JT was arrested early Tuesday morning in Sag Harbor after police spotted him blowing a stop sign and swerving between lanes while he was behind the wheel of a BMW UT.

According to court documents ... JT told police that he had only one cocktail at The American Hotel in town, but he still reeked of alcohol and exhibited other signs of being drunk, such as slowed speech.

Cops said JT failed a field sobriety test and refused to take a breathalyzer. JT also posed for a glassy-eyed mug shot, which was publicly released and spread like wildfire around the world on the Internet.

In court, JT pleaded not guilty to the DWI charge and was released without bail. His defense attorney, Edward Burke Jr., issued a statement ... "[We] look forward to vigorously defending Mr. Timberlake against these allegations. He will have a lot to say at the appropriate time."