WALES flanker Justin Tipuric will tell you that four into three doesn't go in the back row, writes Chris Kirwan.

The Ospreys ace has got used to being back-up to Dan Lydiate, Sam Warburton and Taulupe Faletau on the international stage and a Newport Gwent Dragons player will be able to empathise on Friday night.

The region play their biggest game for eight years against Edinburgh at Murrayfield on Friday when they attempt to go one better than Paul Turner's 2007 team by qualifying for the final of the European Rugby Challenge Cup.

Director of rugby Lyn Jones and head coach Kingsley Jones have a couple of tough calls to make with the back row a particularly welcome headache.

One would imagine that Taulupe Faletau, surprisingly left among the replacements in the quarter-final against Cardiff Blues, will this time wear 8 on his back while Nic Cudd is in pole position at openside.

Nick Crosswell has been superb since arriving from New Zealand and is likely to slot in at blindside but James Benjamin has also been playing out of his skin and gave food for thought as a replacement against Leinster on Sunday.

The 21-year-old from Rogerstone scored two tries in the stunning 25-22 victory against the Guinness Pro12, showing attacking intelligence that could be handy off the bench at Murrayfield.

"We are on such a good run and all the back rows are playing brilliantly. Everyone has got to try and put pressure on each other," he said.

"It's up to the coaches and I am sure whoever they pick will do a good job."

Benjamin got his name on the scoresheet on Sunday but it was Wales and Lions ace Faletau that was star of the show with a sensational display that dragged the Dragons back from 22-8 down.

"You look at Toby in awe because he is everywhere on the pitch. He is involved in every significant part of play," said Benjamin

"He is a great player to play with, in attack and defence. He never stops working and gives us go-forward. For the last try of the game, he ran through three players and put us on the front foot."

Benjamin has made 13 appearances in a breakthrough season that he hopes will feature a final at the Twickenham Stoop on Friday, May 1.

He said: "Leinster was a massive confidence-booster but Friday is cup rugby. Edinburgh lost to Munster but it will have no reflection on the semi-final.

"We've just got to go to Murrayfield, play our hearts out and hopefully get the win."