The Melbourne Rebels have again let a Super Rugby Pacific halftime lead slip, falling to the defending champion Crusaders 43-27 to put a dent in their finals hopes.

In their last outing at AAMI Park, the Rebels led the Blues at the break before the visitors blew them away in the second half.

While Friday night's match was a tighter affair, Melbourne's 12-point halftime lead evaporated with the Crusaders running in four second-half tries.

It was a disappointing end to a memorable week for the club, who were looking to celebrate new deals for head coach Kevin Foote and his two assistants.

It was also a huge blow for the hosts, who entered the match in 10th spot and in dire need of wins.

"24-12 at halftime and then 27 points to three in the second half so very, very disappointed," Foote said.

"It's not good enough for us at home against that team that we could have done something special against so very disappointed.

"There's no excuse for that."

Foote felt his bench players panicked under pressure in the second half which meant their defence fractured, allowing the Crusaders to dictate the match.

Scott Robertson said his team knew chances would come if they bided their time as the game went on.

"In the first half we were in their 22 14 times and only converted twice, so we knew we had opportunities and if we could make them make enough tackles in the second half we would get benefit and we did," the Kiwi coach said.

The Crusaders have battled a huge injury toll but were still fourth on the ladder heading into the contest, with star playmaker Richie Mo'unga turning out for his 100th Super cap.

The visitors had all the ball early but the Rebels showed desperation to keep them out until the 11th minute, when Braydon Ennor sent a long pass out to winger Macca Springer.

To the home side's credit they hit straight back with skipper Brad Wilkin diving across the line from the back of a ruck.

And they were in again three minutes later when No.8 Vaiolini Ekuasi scooped up the ball, lost by Crusaders centre David Havili after a big hit by Josh Canham.

Ekuasi, who also extended his Rebels deal this week, had to run 90 metres to touch down.

Halfback Ryan Louwrens then got amongst the spoils for Melbourne to take a healthy 24-12 lead to the sheds.

They were notably wary after their halftime lead over the Blues turned into an ugly 54-17 loss.

And their worst fears were realised with two second-half tries seeing the Crusaders take a 26-24 lead in the 63rd minute.

The Rebels weren't rattled at this stage and went ahead again through a Reece Hodge penalty kick.

But with likes of All Blacks centre Jack Goodhue coming off the bench the Crusaders kept attacking and reserve hooker Ioane Moananu shrugged off defenders to storm over.

A Mo'unga penalty gave his team a nine-point buffer and then he set up a try for reserve back Dallas McLeod.

The visitors rubbed further salt into the wound with an 82nd-minute score to also collect a bonus point.