Rebels to stay grounded after soaring to top of Aussie conf.

The Melbourne Rebels are vowing to stay grounded despite soaring to the top of the Australian conference with an historic Super Rugby triumph over the NSW Waratahs.

The Rebels humbled the Waratahs 21-17 at Allianz Stadium last night to record their first-ever win in Sydney and join the Brumbies as surprise equal conference leaders.

"It's a significant result for the club and the Rebels organisation," jubilant coach Tony McGahan said.

"These results are really important to what we create. We don't have a long history like the Waratahs, so for us to accumulate these wins, especially away from home, is really important for the club."

Defying a daunting early-season travel schedule, the Rebels have posted wins in Perth, Tokyo and now one in Sydney against the 2014 champions to emerge as genuine finals contenders.

McGahan, though, said co-captain Nic Stirzaker and fellow team leaders including All Black World Cup winner Adam Thomson would ensure the Rebels will not be getting carried away.

"It gives us confidence," McGahan said.

"But I think the group - their humility and the way they go about their business - certainly won't allow us to go any further than where we are at the moment.

"There's not a lot of rugby down in Melbourne, so we don't get too ahead of ourselves. There's not much (rugby) to read, to be honest."

The Waratahs' sapping home defeat leaves the 2014 champions nine competition points adrift of their two big rivals ahead of a second bye next weekend and a massive conference derby with the Brumbies in Sydney in a fortnight.

With a two-from-five start to their campaign, the Waratahs face an almighty battle to drag themselves back into finals contention under first-year head coach Daryl Gibson, who will also likely come under increasing pressure.

Tries to flanker Jack Dempsey and centre Matt Carraro gave the Waratahs a chance to snatch victory late, but it would have been an injustice.

The damage was done in a bumbling first half from the Tahs, when soft tries to five-eighth Jack Debreczeni and prop Toby Smith, plus a conversion and three penalty goals from Debreczeni earned the Rebels a 21-3 advantage at the break.

"Some of that stuff out there was rubbish," Gibson fumed on Fox Sports during the interval.

"I want to see some pride in the jersey. Show the people of NSW what we can do."