Stand-in hooker John Ulugia had the last laugh after scoring the match-winning try in the NSW Waratahs' vital Super Rugby win over the Western Force in Sydney on Saturday night.

Filling in for Wallabies star Tatafu Polota-Nau, Ulugia wriggled over in the 70th minute to earn the injury-hit Waratahs a 20-15 triumph and a place back in the top six.

The Highlanders' 20-7 loss to the Chiefs earlier on Saturday in New Zealand allowed the Waratahs to edge back into the finals zone on points differential.

Five penalty goals from Force centre James O'Connor had given the tourists a 15-13 advantage as the clock wound down at the SFS, but Ulugia - touted mid-week as a potential Waratahs weak link - saved NSW blushes and possibly their 2011 season.

NSW captain Dean Mumm hailed NSW's third-choice hooker a hero after Ulugia silenced the critics who predicted his lineout throwing in particular would be picked off by Force skipper Nathan Sharpe.

"Ulugia was fantastic," Mumm said.

"His whole game was very, very good. There was a lot of perceived pressure on him - I'm not sure how he felt - but he certainly stood up."

Ulugia modestly deflected the praise to his teammates.

"I'm proud of my performance, but it's not about individuals."

It was a special win also for former Force star Ryan Cross, who, having been bagged by his ex-teammates for questioning their mettle under pressure earlier in the season, notched NSW's only other try.

With the `Tahs trailing 9-6 early in the second half, a Kurtley Beale penalty goal attempt ricocheted off the left upright and Cross pounced to score and put his side in front for the first time.

"He's probably chased through about 50 of those kicks in his time and never got one. Tonight he got his reward," NSW coach Chris Hickey said.

"Some games you win with skill and others you win with will."

The victory was just the tonic for the Waratahs, who enjoy the bye next weekend and a guaranteed four competition points before hosting the last-placed Lions the following round.

In a tight first half dominated by strong defence and big hits, O'Connor nailed three penalties to Beale's two to leave the Force three points up at the break.

Beale's conversion of Cross's fortuitous try gave NSW a four-point buffer before O'Connor nudged the Force back ahead with his fourth and fifth penalty goals.

Ulugia, though, had the final say with the Waratahs turning down the opportunity to slot a last-minute penalty goal to further boost their for-and-against record.

"It was certainly tough," Mumm said.

"Every win is important. That's two in a row now and we just need to keep winning."

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