PARIS- Ernests Gulbis has condemned Roger Federer to his worst French Open defeat in a decade as Novak Djokovic remained calmly on course for a maiden Roland Garros title.
Gulbis, the controversial Latvian, beat the fourth-seeded 2009 champion 6-7 (5/7) 7-6 (7/3) 6-2 4-6 6-3 as Federer, 32, suffered his earliest loss in Paris since 2004 when he was demolished on Sunday in the third round by Gustavo Kuerten.
Victory would have put Federer into a record 42nd Grand Slam.
He unleashed 13 aces and 53 winners with Federer undone by an uncharacteristic 59 unforced errors as he lost a five-setter at Roland Garros for the first time.
"I was all over the place,I am disappointed not to win. I have a lot of regrets.
"But he did a good job of hanging around and coming back. I just wish I could have played better."
Gulbis, who took a controversial medical timeout in the fourth set, was delighted by his win.
"It was a tough match and I'm sorry as I know that most of you wanted Roger to win."
The Latvian incurred the wrath of the pro-Federer centre court crowd when he took a medical timeout to treat lower back pain at 2-5 down.
"I'm honest, I'm not big on medical timeouts. I don't like to take it, but I take it when it's really necessary. It probably was my third medical timeout in my life." Gulbis set up two match points with his 13th ace and claimed his famous victory when Federer slapped a backhand wide.
Djokovic, the 2012 runner-up who needs a French Open title to complete a career Grand Slam, swept into the quarter-finals with a one-sided 6-1 6-4 6-1 win over top home hope Jo-Wilfried Tsonga.
"It was a very good match for me. I prepared well tactically with my team," said world number two Djokovic.
"I started with much intensity and quality and happy with my game today."