Jennifer Lopez and Ben Affleck's Romantic Afternoon Halted By Flat Tire

Jennifer Lopez and Ben Affleck's romantic afternoon had a wrench thrown in it ... or more accurately a tire -- 'cause one of theirs popped and stopped their date

The lovebirds were rollin' around Los Angeles Saturday in a silver BMW when they suffered a flat tire, quickly bringing their couple's outing to an unfortunate standstill.

Bennifer hopped out to check the damage -- with Ben in a flannel and baseball cap while J Lo rocked a tight black turtleneck and matching leggings.

Affleck and Lopez both got their hands dirty, leaning over the car -- with Ben's shirt lifting to reveal his infamous back tattoo -- but they ultimately weren't able to fix the problem.

Eventually, Lopez and Affleck just had to leave the car ... calling for a ride to come pick them up and leaving the Beamer behind as they headed for greener pastures.

Unclear who picked up the BMW or if it was taken to a shop, but it's far from the first time Ben's had car trouble ... with his luck seeming more than a little worse than the average motorist on the road.

Remember last year when Ben's classic Cadillac broke down during a heat wave in the City of Angels? Or when his son Samuel accidentally backed a rental Lamborghini into another car?

Yeah, certainly seems like bad luck seems to plague the movie star everywhere he drives.

Seems like the rest of the day went just fine for the couple ... who were at the Lakers game last night -- apparently it's gonna take more than a flat than to keep the couple from courtside seats.