Romania coach Lynn Howells ordered his team to "pull your socks up" at half-time and the East Europeans pulled off the biggest comeback in World Cup history against Canada on Tuesday.

Romania captain Mihai Macovei got two second half tries as his side fought back from 15-0 down to beat their stunned Canadian opponents 17-15.

Howells team could just sneak third place in Pool D and an automatic qualifying place for the 2019 World Cup if they beat Italy on Sunday.

Canada, on the other hand, ended their World Cup with four straight group defeats for the first time.

The Canadians could not believe their luck after DTH van der Merwe scored a try for the fourth straight match, joining an elite group, including All Black legend Jonah Lomu, who have scored in every group match at a World Cup.

Romania were reduced to 14 men for part of the first-half when Catalin Fercu was sin-binned for taking out Nick Blevins in mid-air.

But Van der Merwe finished off an excellent play created by wing Jeff Hassler's surge through the Romanian defence to touch down.

And despite Howell's rocket, Canada came out straining at the leash in the second period. Hassler got a deserved try of his own in the 44th minute, Nathan Harayama making the initial inroad.

Then the Romanian storm hit.

Their first try stemmed from their scrum rocking their opponents back on their heels and over the line. Macovei claimed the try and Florian Vlaicu converted.

Canada might have held out but for a moment of madness by Jebb Sinclair when eight minutes from time he became the third Canadian to be yellow-carded in the tournament.

Two minutes later Macovei peeled off a scrum for his second try.

Vlaicu converted for 15-14 and set up a nerve-wracking final five minutes which he rounded off with a superb long range penalty to take the lead. That took Vlaicu to a national record of 636 points and Romanian celebrations erupted.

Howells said he had no doubt that his side could win and his half-time message had been direct: "Pull your socks up."

"The disappointing thing for me is that we played so poorly in the first half and that is not something that is acceptable," said the Welshman.

"We came in with a game-plan and we knew what we had to do against Canada.

"We had to stop the quick ball and I think we became more effective at that in the second half. Also, I think Canada made more mistakes and it allowed us to get the scrum game going, driving game going. That really changed the game."

Howells said the team would be allowed a celebratory beer but it would not be allowed to spoil preparations for Sunday's game in Exeter.

"It will be in the team room and we'll have full control on what they do drink."

Romania's captain praised scrum coach Marius Tincu for staying with the team after his mother died three days earlier. "He decided to stay with the team. All of us had our thoughts and hearts with him," said Macovei.

Howells insisted that in spite of Italy's higher ranking, Romania could still pull off another upset.

"Semi-final won, now we play the final," Howells declared.

"There is still an opportunity, in rugby anything is possible. Against Italy the players understand they are playing a tier-one nation and they have to lift their game."