Roger Federer became the oldest world number one in tennis history after he beat Robin Haase at the Rotterdam Open.
The 36-year-old replaces Rafael Nadal, 31, at the summit, as the Spaniard recovers from a thigh injury.
Federer's prospects looked slim when he lost the first set, but he dropped just two games thereafter to claim a 4-6 6-1 6-1 win and reach the semi-finals.
The 20-time Grand Slam champion will face Italian Andreas Seppi or Russia's Daniil Medvedev in the last four.
At the end of the match, Federer sat down in his chair and wiped away tears from his eyes, before returning to the court to take the acclaim from the crowd and being awarded a trophy for his achievement.