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Denver Nuggets star Ty Lawson got busted for DUI in Los Angeles last night -- his second DUI arrest this year.

TMZ Sports has learned Lawson was pulled over by CHP for speeding on the 101 Freeway early this morning ... and officers determined he showed signs of intoxication ... so they gave him a field sobriety test.

Didn't go so good for Lawson. He was arrested around 2:30 AM.

Cops say during the arrest, Lawson identified himself as an NBA player -- and was carrying $6,000 IN CASH on his person.

We actually spoke to Lawson as he and his GF Ashley King (former "Bad Girls Club" star) were leaving Le Jardin nightclub in Hollywood -- moments before they jumped on the freeway. Interesting ... we talked marijuana with him.

He's still in jail right now. His bail's been set at $5,000.