The Rebels' celebrations turned sour as they sank to a disappointing 40-18 loss to the Highlanders in their Super Rugby clash in Melbourne.

Like a bottle of champagne that lost its fizz, the Rebels produced a flat performance at AAMI Park, unable to translate their off-field success this week with the signing of Wallaby and NSW star Kurtley Beale and emerging young players Nick Phipps and Hugh Pyle.

Lock Pyle did manage to score but that didn't come until the 65th minute when the win was out of reach.

Their trademark aggressive defence was missing - Highlanders winger Kade Poki skipped through seven Rebels to score in the second half - while they barely threatened in attack.

Usually one of their most consistent performers, English five-eighth Danny Cipriani had an off night but he wasn't alone.

Skipper Stirling Mortlock was a late withdrawal with a hip injury and the new centre combination of Mark Gerrard and James Hilgendorf, who hadn't played since round one, struggled.

The Highlanders suffered an early blow when they lost five-eighth Colin Slade four minutes into the match with a cut head and possible jaw injury.

The New Zealanders weren't flustered but his replacement Robbie Robinson could only managed to kick four goals from 11 attempts.

Scoring six tries, it didn't matter.

The Highlanders had a 22-6 lead at the break thanks to tries by Adam Thomson, Alando Soakai and Siale Piatau, whose effort came in the final minute of the half.

Both Piatau and Thomson again crossed in the second half, the latter diving over in the corner with 10 minutes remaining after a burst from the halfway line.

Veteran Rebels prop Greg Somerville barrelled over for a try in the 78th minute but there was little else for the crowd of 18,739 to cheer about.

Rebels coach Rod Macqueen rated it on par with their worst performance of the season, which was a 43-0 loss to the Waratahs in the opening round.

"That rates with our performance against the Waratahs in the first game," Macqueen said.

He said the team spoke before the match about maintaining momentum after the bye.

"We're aware you can come out after the bye and be flat ... we thought about and trained hard but we didn't play well."

While he gave credit to the Highlanders, who troubled the home side with their intensity at the breakdown, Macqueen said the late loss of Mortlock proved too troublesome for the side to overcome.

"We really didn't have a chance to train with that combination during the week ... it didn't gel and as far as the organisation of the background it just wasn't good."

Mortlock is expected to be fit for next round's clash with the Blues in Auckland although there's some doubt over Pyle, who looks to have an adductor injury.

For the Highlanders, Slade is set to undergo surgery on his broken jaw in Melbourne before returning to Dunedin.

Coach Jamie Joseph, whose team now has racked up six wins and only two losses, said it was a big blow for the team on an otherwise impressive night.

"He broke his jaw in the first pre-season game and he's only played a game and a half and he took a bang," Joseph said of Slade.

"He's a key player for us and also a key player for the All Blacks ... it's really disappointing."

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