The Western Force have overcome the late dismissals of two players to score a match-winning penalty after the final siren in a remarkable 21-18 victory over Moana Pasifika at HBF Park.

Scores were level at 18-18 in Saturday night's Super Rugby Pacific match when the Force had Ollie Callan red carded in the 73rd minute and Siosifa Amone also then sent off with a yellow three minutes later.

But instead of wilting under the numerical disadvantage, the 13-man Force pulled off a series of clutch plays at the death to secure the win in front of 6497 fans.

Scrumhalf Issak Fines won a crucial penalty at the breakdown to give the Force good field position, and although Bryce Hegarty's 45-metre penalty attempt in the 79th minute missed, the home side kept pushing.

A smother from Tim Anstee put Moana under the pump and forced a knock-on error, and the Force won a scrum penalty after the final siren.

Hegarty nailed the penalty from eight metres away straight in front to secure the win.

The result was in stark contrast to last week, when the Force were pumped 71-20 by the Queensland Reds.

"It is significant, because sometimes winning ugly is about winning," Force coach Simon Cron said.

"The fight the boys showed was really positive.

"The area they will find hard to watch is the opportunities we did create and then gave them the ball back."

The Force leaked 10 tries against the Reds, and it took Moana just 28 seconds to touch down on Saturday night in an ominous sign.

The dazzling play started with a dribble from Moana's defensive 22 and was followed by a series of sharp passes to allow Fine Inisi to score.

The scoreboard read 15-6 in the 25th minute when Moana hooker Samiuela Moli touched down from a rolling maul.

Moana prop Sueten Asomua was yellow carded shortly before halftime, and Force hooker Folau Fainga'a scored on the very next play from a rolling maul.

Scores were level in the 61st minute when the Force swung it wide after a rolling maul and George Poolman touched down in the corner.

Hegarty missed the sideline conversion attempt, and the Force were down to 14 men when Callan was sent off in the 73rd minute for a no-arms tackle that resulted in his shoulder colliding with his opponent's head.

Amone joined him on the sidelines a few minutes later for a high hit, but the Force kept pushing for the win and finally got the result.

"It's one we let slip," Moana coach Aaron Mauger said.

"We've got to be better in those moments. We couldn't execute our basics. It's hard to play when you're not catching the ball."