MONTE CARLO, Monaco (AFP) - Roger Federer joined holder Stan Wawrinka as an upset victim at tennis' Monte Carlo Masters on Thursday, as the 2014 finalist lost 4-6, 6-7 (5-7) to France's Gael Monfils.
Earlier, Grigor Dimitrov stunned seventh seed Wawrinka as he beat the Swiss 6-1, 6-2 in the third round.
World No. 2 Federer missed the chance to reach the last eight, weighed down by nearly 40 unforced errors against his French opponent.
The exit of 2014 Australian Open champion Wawrinka came a year after he won his first and only Masters 1000 title here, beating his compatriot Federer in the final.
Wawrinka was well off his game, finishing in 54 minutes with 41 unforced errors and just four winners against ninth seed Dimitrov.
The ninth-ranked player is now in danger of losing his top 10 place.
Federer reached the final last year for the fourth time in his career, and the loss is a setback just six weeks before the second Grand Slam of the season in Roland Garros.