Unheralded Spaniard Guillermo Garcia-Lopez caused the biggest shock of the French Open when he knocked out Swiss third seed Stan Wawrinka 6-4 5-7 6-2 6-0.

The Australian Open champion, who was tipped as a possible champion in Paris, struggled throughout in a mistake-strewn performance that saw him produce 61 unforced errors.

Garcia-Lopez laid down the gauntlet from the outset by breaking twice and putting Wawrinka in an early hole by taking the first set in 36 minutes on Monday.

The Swiss number one then had to dig deep to level the match when he broke at 6-5 up in the second despite firing an uncharacteristic 17 unforced errors.

The Spaniard remained unruffled however and broke the Wawrinka serve for the fourth time in the opening game of the third set to seize the momentum he never relinquished.

When he wrapped it up 6-2 under fading light on a rain-hit day, the writing was on the wall for the Swiss star.

The 29-year-old was increasingly frustrated and out of sorts as Garcia-Lopez continued to dominate a match he never looked like losing.

Wawrinka, who has a reputation as a great five set player, never got that far as he collapsed 6-0 in the decider to hand Garcia-Lopez arguably the finest win of his career.

The 30-year-old, who came into the tournament ranked 41 in the world, can now look forward to a second round match against Frenchman Adrian Mannarino.