David Ferrer defeated fellow Spaniard and world number one Rafael Nadal 7-6 (7/1), 6-4 in a hotly disputed quarter-final at the Monte Carlo Masters on Friday.
Ferrer, 32, who reached a career-high world number three ranking last year, outlasted his rival and good friend in a marathon 75-minute first set to seize the advantage.
He then broke Nadal's serve twice to lead 5-2 before a lapse in concentration allowed the Mallorcan left-hander to claw his way back into the set.
However, on his second attempt to serve out for the match, Ferrer used a series of powerful baseline shots to keep Nadal pinned to the back of the court and closed out the victory on his first match point.
Nadal had reached the final in each of the last nine years - he won the tournament a record eight times in a row before losing last year's championship match in straight sets against Serbia's Novak Djokovic.
Nadal's only other defeat in Monte Carlo dates back to 2003 when he was beaten in the third round by Argentine Guillermo Coria.
Ferrer meanwhile ended a 10-game losing streak against Nadal, including the 2011 Monte Carlo final.
Sixth seed Ferrer will play a Saturday semi-final against Swiss third seed Stanislas Wawrinka, who beat Nadal for the Australian Open title in January.
Wawrinka booked his place by beating Canadian Milos Raonic 7-6 (7/5), 6-2 earlier on Friday.