ANDY Murray returns to the daily grind of life on tour this afternoon, just days after retaining his Olympic title. The Scot, who beat Juan Martin del Potro in the final in Rio, had a first-round bye in the Western & Southern Open in Cincinnati, but now faces a second-round match against either Ivo Karlovic or Juan Monaco. Murray, the No 1 seed, beat Monaco in straight sets in the second round in Brazil.

At the other end of the draw, former French Open champion Stan Wawrinka opens his campaign against Jared Donaldson of the United States. Rafael Nadal and Milos Raonic are among the other top players in action.

Nadal will open his campaign against Pablo Cuevas, who downed Sam Querrey 4-6 7-6 (7/5) 6-3 in the first round. France's Julien Benneteau upset number 10 seed David Ferrer 6-4 2-6 6-4 while Marin Cilic defeated Viktor Troicki 6-3 6-4 inside 62 minutes.

Elsewhere, Grigor Dimitrov edged out Gilles Simon 6-1 6-3 and Kevin Anderson progressed when Alexandr Dolgopolov retired hurt at 7-5 0-0. Nick Kyrgios reached the second round for the first time in his career with a 6-2 7-5 win over Lucas Pouille.

While the main purpose for Murray and his rivals is to prepare for the US Open, there is a greater immediate goal for Angelique Kerber - taking over Serena Williams’ world No 1 spot. The German, who like Murray travelled to Ohio straight after winning Olympic gold, will take over from the American at the top of the rankings if she wins this week.

Williams, 34, revealed she had opted against accepting her wild-card place at this tournament due to a shoulder injury. She has been ranked world No 1 for 183 consecutive weeks.

Kerber's second-round opponent will be either Kateryna Bondarenko or Kristina Mladenovic, while Jelena Ostapenko enjoyed a memorable win on Monday.

The 19-year-old former junior Wimbledon champion produced a stunning comeback to defeat Anna Karolina Schmiedlova 1-6 7-6 (8/6) 7-6 (7/5) and she will next meet Karolina Pliskova of the Czech Republic.

Lesia Tsurenko downed qualifier Shuai Zhang 6-3 6-3 as American hopeful Coco Vandeweghe defeated former French Open finalist Sara Errani 4-6 6-3 6-4.

Elsewhere, Daria Gavrilova ousted Caroline Garcia on the back of a 7-5 6-3 triumph and Donna Vekic surprised Ana Ivanovic to win 6-4 6-2. Christina McHale won 6-2 6-2 success against qualifier Saisai Zheng.