PARIS -- Current world No 1 Rafael Nadal announced his withdrawal from the ATP Paris Masters 2018 due to an abdominal problem, while seeded players unsurprisingly moved through the second round here on Wednesday.

Nadal's withdrawal is set to send Novak Djokovic back to the top spot in the upcoming ATP rankings for the first time in two years.

"The last few days I started to feel a little bit the abdominal, especially when I was serving," Nadal told a news conference.

"I was checking with the doctor and the doctor says that is recommended to not play, because if I continue the abdominal maybe can break and can be a major thing, and I really don't want that," he added.

Nadal was expected to make his return in Paris after retiring in the US Open semifinals due to a knee injury. He was scheduled to face his fellow Spanish Fernando Verdasco in the second round on Wednesday afternoon, but made his decision to withdraw from the competition just prior to the duel.

Tunisian Malek Jaziri, in place of Nadal as a lucky loser, stepped up to see off Verdasco 7-6 (5), 1-6, 6-3.

Third-seeded Roger Federer enjoyed a walkover into last 16 as his opponent Milos Raonic from Canada withdrew from the competition due to an elbow injury.

The Swiss legend will next face Fabio Fognini, who also benefited a walkover from his Hungarian opponent Marton Fucsovics' withdrawal.

No 6 seed Dominic Thiem got over home crowds' support to eliminate Frenchman Gilles Simon in straight sets.

Thiem, the 2018 Roland Garros runner-up, took advantage of his high-quality serves to snatch four games in a row before building a commanding 5-1 lead, but the home favorite regrouped and responded by winning three games in a row. Then Thiem steadied his nerves for a 6-4 first set win with an ace.

The Austrian was well on track to victory with five games in hand in the second set. Although Simon triumphed the following two games, Thiem managed to convert his second match point at 6-2.

Thiem controls his own destiny at No 8 in the ATP Race to London, while Kei Nishikori and John Isner, two chasers for ATP Finals spots, also marched through Wednesday's match.

Nishikori overcame Adrian Mannarino of France 7-5, 6-4. Isner beat Mikhail Kukushkin of Kazakhstan 6-3, 6-7 (2), 7-6 (1).

For a chance to qualify for the Finals, Nishikori needs to reach the semifinals and Isner must advance to the final at the Paris Masters.

Defending champion Jack Sock saw off French veteran Richard Gasquet 6-3, 6-3, seeing no Frenchman through the singles second round.

Other prominent names like Alexander Zverev, Kevin Anderson and Grigor Dimitrov also secured their berths in Thursday's round of 16.