Daniil Medvedev of Russia retained his position at the top of the Association of Tennis Professionals (ATP) rankings published on Monday

The men's tennis world No. 1 player won his first title since claiming the U.S. Open almost a year ago, when he roared past defending champion Cameron Norrie of Britain in the final of the hardcourt tournament in Los Cabos, Mexico.

With over 1,000 points clear of the injured Alexander Zverev of Germany, Medvedev flew to Canada to defend his title from last August.

Medvedev said on Monday he will carry on as usual at this week's ATP Montreal Masters despite the absence of his major rivals.

The top seed will not have to face Novak Djokovic due to the Serb's refusal to take the COVID-19 vaccination.

And Rafael Nadal of Spain dropped out before the start as his abdominal injury from Wimbledon flared up during training in Spain.

Roger Federer's presence has not even been factored in yet as the Swiss, who turned 41 on Monday, puts finishing touches on his knee surgery recovery.

"If the Big Three are in the tournament, they are the favorites straightaway," he said.

"They win a lot of tournaments, almost every tournament they play, so there is no surprise when we make them favorites," he added.

"For me, it doesn't change much if they're here or not. My goal is to win the tournament. No matter who I play, I just want to win the match."

China's tennis players shined at two ATP events this weekend.

Zhang Zhizhen defeated Italy's Andrea Vavassori 2-6, 7-6, 6-3 in three hours to win the ATP Challenger Tour in Cordenons, Italy, while Shang Juncheng won the Lexington Challenger title after beating Emilio Gomez of Ecuador 6-4, 6-4 in the final in Lexington, Kentucky, the United States.

It was the third Challenger Tour title for Zhang. The Challenger Tour is the second-tier competition behind the ATP Tour. Young players need to earn ranking points to qualify for the main draw of the ATP Tour.

In women's tennis, Serena Williams dropped huge retirement hints after winning her first singles match in 430 days.

She stepped onto a hardcourt for the first time in a year and a half on Monday and fought through for a 6-3, 6-4 victory over Spain's Nuria Parrizas Diaz.

The 40-year-old American was competing in only her second match this season in defeating the 57th-ranked lucky loser to reach the second round.

The relieved 23-time Grand Slam winner said the victory boosted what had been fragile confidence after her long periods of recent competitive inactivity.

"I guess there's just a light at the end of the tunnel. I'm getting closer to the light," she said.

"I can't wait to get to that light. I love playing though, it's amazing but I can't do this forever. Sometimes you just want to try your best to enjoy the moments and do the best that you can."

(With input from agencies)