Andy Murray swerved a monumental upset against home qualifier Mathias Bourgue at the French Open, but his five-set comeback victory only cast further doubt on his title-winning credentials.

The world No.2, who was also pushed the distance by veteran Radek Stepanek in the opening round, suffered an alarming mid-match dip before coming through 6-2 2-6 4-6 6-2 6-3. The Brit will face big-serving Ivo Karlovic in the third round, the 37-year-old Croatian having come through his own five-set epic with a 12-10 win in the decider.

"You can't play too many matches like this if you want to go far in this tournament. I hope to win the next one a little bit faster," said Murray courtside.

Murray's scare came out of nowhere: he looked in complete control after taking the first set and then broke Bourgue in the Frenchman's opening service game of the second set.

But rather than have the match in the bag, Murray suffered an unlikely implosion to gift his 22-year-old opponent a route back into the match as every aspect of his game disintegrated.

Bourgue took full advantage, reeling off eight straight games to transform Murray's advantage into one of his own. And the Frenchman didn’t let up. He might be ranked 164 in the world but, roared on by a vivacious Philippe Chatrier, Bourgue produced shots that would have delighted a top 10 player as he stormed into a two sets to one lead to leave Murray one set away from arguably the most damaging defeat of his career - and what would have been his earliest exit at a grand slam since his first-round defeat at the 2008 Australian Open.

Murray dug deep to survive an onslaught in his opening service game in the fourth set as the impossible started to look probable, before steadying to break twice and force a decider.

He raced into a 5-1 lead as Bourgue fatigued and although another wobble briefly gave the Parisians hope, he belatedly served it out to keep his hopes of a maiden Roland Garros title alive.

Alive, yes, but not thriving: talk of Murray being joint-second favourite alongside Rafa Nadal now appears to have been hugely optimistic.

There is still a lot of tennis to be played, but the Scot will have to play his way into form quickly. "I was thinking 'what happened?' I was leading 6-2 2-0 and from then on he started playing unbelievably and I was finding it very hard to win points, let alone games," Murray added.

Bizarrely, the encounter with Karlovic could provide welcome relief for Murray. The Croatian - the all-time record holder for aces served on tour - is a tough customer, but at age 37 the fact that he endured such a lengthy thriller with Australia’s Jordan Thompson will surely hurt his hopes.

He might have won 12-10 in the decider, but will surely be fatigued - and a match of short, sharp points is to be expected. After more than seven hours on court, it could prove the perfect remedy for the British No.1.

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