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Kacey Musgraves‘ tour bus came to the rescue after a man’s pickup truck rolled over on an Arizona highway … TMZ has learned.

The Arizona Department of Public Safety tells TMZ … troopers responded to a Toyota Tundra rollover on Southbound U.S. 93 just outside Kingman around 12:15 PM Friday … and eyewitnesses say the pickup veered off the road and flipped.

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We’re told one of Kacey’s tour bus drivers stopped to help the man and stayed with him until paramedics arrived. Kacey has a show in Phoenix on Saturday, and it sounds like her tour buses were in the right place at the right time.

According to officials the bus driver was a former firefighter and actually helped extricate the driver.

Folks who were there say the driver’s wife was following behind in another vehicle with their dog … and the pup is safe.

Officials tell TMZ … the driver was alert and responsive after the crash and was transported to a local hospital with minor injuries.

Sources close to Kacey tell TMZ … the singer was NOT on the tour bus when it pulled over, and the tour will continue as scheduled.

We’ve reached out to reps for Kacey for comment … so far, radio silence.