At the age of 36, Roger Federer is now two wins away from reclaiming the top ranking for the first time in six years.
Federer began his campaign at the ABN AMRO tournament on Wednesday with a flawless performance, defeating Ruben Bemelmans 6-1, 6-2 in just 46 minutes.
The 20-time Grand Slam champion was in complete control against the Belgian qualifier. The Swiss hit six aces, dropped only four points on his serve, and broke Bemelmans four times in the first round.
Federer will replace his old rival Rafael Nadal at No. 1 if he reaches the semifinals at the indoor tournament. By achieving the feat, he would also become the oldest top-ranked male player. Andre Agassi holds the record, at 33 years, 133 days old.
Federer next plays Philipp Kohlschreiber, a player he has never lost to in 12 previous matches.
Earlier, David Goffin eased into the quarterfinals by defeating Feliciano Lopez 6-1, 6-3. Goffin had nine aces and dropped just two points behind his first serve to extend his unbeaten record against Lopez to 3-0.
The seventh-ranked Goffin, who beat Nicolas Mahut in straight sets in his previous match, will next face sixth-seeded Tomas Berdych.
Second-seeded Grigor Dimitrov beat Yuichi Sugita 6-4, 7-6 (5) in the first round and Robin Haase won an all-Dutch contest against Thiemo de Bakker 6-2, 6-2. Dimitrov and Haase were joined in the second round by qualifier Pierre-Hugues Herbert, who advanced after Richard Gasquet retired while trailing 3-1.
(With AP Inputs)