Wimbledon champion Novak Djokovic booked his place in the second round ©Getty Images

Wimbledon champion Novak Djokovic and Serena Williams of the United States booked their places in the second round of the men's and women's singles events respectively on the opening day of the Cincinnati Masters.

Djokovic, a 13-time Grand Slam winner, beat American Steve Johnson 6-4, 7-6 at the Lindner Family Tennis Center.

The 31-year-old Serbian will next face Adrian Mannarino of France, who overcame Italian Marco Cecchinato 6-7, 6-2, 7-6 in a hard-fought contest.

Britain's Andy Murray, who is continuing his return to the circuit after a long break to recover from a hip injury, was among the high-profile casualties on day one as he lost 6-1, 1-6, 6-4 to Frenchman Lucas Pouille.

Pouille, the world number 17, will take on Leandro Mayer after the Argentinian ousted American Michael Mmoh 6-4, 1-6, 6-4.

Swiss star Roger Federer, seeded second, is due to be in action tomorrow as he faces Peter Gojowczyk of Germany.

The 20-time Grand Slam winner is the top seed following the withdrawal of Spaniard Rafael Nadal, who won the Rogers Cup in Toronto yesterday.

Serena Williams was among the first-round winners in the women's singles draw ©Getty Images
Serena Williams was among the first-round winners in the women's singles draw ©Getty Images

In the women's event, Williams returned to form in style as she thrashed Australian Daria Gavrilova 6-1, 6-2 in just 65 minutes.

"I realised after Wimbledon that this is a journey for me," Williams, a 23-time Grand Slam winner, said. 

"It's going to come and I'm taking it one day at a time. 

"I'm just fortunate to be back here on these courts playing tennis."

The 36-year-old American will play eighth seed Petra Kvitová of the Czech Republic in the next round.

Alize Cornet of France sprung a first round surprise as she dispatched 11th seed Jeļena Ostapenko of Latvia 1-6, 7-5, 6-0.

The tournament is due to continue tomorrow.

It is an Association of Tennis Professionals Masters 1000 tournament and a Premier 5 event on the Women's Tennis Association tour.