The Waratahs were on track for their first win of the Super Rugby AU season when unheralded flyhalf Ben Donaldson nailed his sixth kick of the night to give the visitors a 30-21 lead.

But the Force refused to give up, with a Jordan Olowofela try in the 72nd minute and a clutch Miotti conversion from the sideline reducing the margin to two points.

The Waratahs lost a line-out with just seconds remaining to give the Force one final chance of victory.

The Force unleashed phase after phase after the final siren in a bid to find the winning points, and they got their chance when NSW were penalised for offside.

Miotti stepped up to the plate and calmly slotted the 21m penalty from in front to send the 9,253 crowd into raptures.

The result lifted the Force into third spot, three points clear of the Rebels.

But given the Rebels have two games to play and the Force just one, the Melbourne-based franchise is still a good chance to snare third spot.

"We were so grateful that we got that result," stand-in Force skipper Kyle Godwin said.

"We worked 20-plus phases to get that result, and we had a lot of confidence in Domingo. He's a great kicker, and he's really cool and calm and composed under pressure."

The win was the Force's first Super triumph in Perth since they beat the Waratahs 40-11 in 2017.

"The boys are gutted," Waratahs co-coach Jason Gilmore said.

"They put in a good shift, particularly in that second half. It was within our grasp at the end.

"To lose it after fulltime, and particularly to a penalty, after we had the opportunity to shut the game down as well - that one hurts."

The Waratahs were on the back foot early after flanker Lachie Swinton was yellow carded for a dangerous tackle in the third minute.

The Force scored almost immediately when prop Tom Robertson barged through two players to cross.

Waratahs No.8 Will Harris pulled a try back in the 16th minute, and flyhalf Donaldson faced an embarrassing moment when he continually tried and failed to get the ball to balance on the tee for the conversion attempt.

With his allotted time running out, Donaldson had no choice but to unleash a drop kick, and he nailed it through the middle.

Force hooker Feleti Kaitu'u put the home side ahead again in the 25th minute when he ripped the ball out of teammate Santiago Medrano's hands while the prop was being tackled, and then sprinted 33m to the line.

NSW came out firing in the second half, with fullback Jack Maddocks and former Force winger Alex Newsome crossing within minutes of each other to give the visitors a 24-18 edge.

But a late rally from the Force got the home team over the line, despite the heroics of Donaldson who nailed a perfect three-from-three penalties, and three-from-three conversion attempts.

Australian Associated Press