Al Jazira had lost ground in the race for the title with defeat at home to Al Dhafra last weekend, but failed to recover their form at the defending champions.
Omar Abdulrahman put the home side in front after 17 minutes, before Asamoah Gyan curled in a second from the edge of the penalty area 15 minutes later.
Manuel Lanzini pulled one back shortly before the interval but, despite having Mohanad Salem sent off for a second bookable offence with three minutes left on the clock, Al Ain clung on for victory.
Al Jazira's defeat went relatively unpunished, though, as their three closes challengers failed to register victories.
Two of those sides - Al Wahda and Al Shabab - played out a 1-1 draw on Sunday, while Al Nasr were held to the same scoreline by lowly Ajman.
There was not let-up for basement club Al Ittihad Kalba, who suffered a 6-1 home thumping at the hands of Al Wasl, and Al Fujairah slipped to 12th with a 4-0 loss at Al Ahli.
Al Sharjah continued their revival with a 5-2 win at Bani Yas, taking them to three victories on the bounce, while Emirates and Al Dhafra played out a goalless draw.
'I won the World Cup and I said to myself, I've done it all, I need to keep feeling emotions': Raphael Varane opens up on why he had to leave 'indescribable' Real Madrid for Manchester United
'When I see Phil Foden play, he just seems like a shy lad - that holds him back a little bit. He has been tried in every position, but he just hasn’t performed': Ex-England star makes bold claim about Manchester City man
