Andy Murray and Rafael Nadal were winners but six seeds were beaten in a day of upsets in the second round at the Rogers Cup in Montreal on Thursday.
After a long rain delay Germany's Sabine Lisicki made quick work of Venus Williams, strolling into the second round of the Rogers Cup on Monday after routing the American 6-0 6-3.
The US Open champion has pulled out of the Rogers Cup event in Montreal.
Sania Mirza and her Polish partner Marta Domachowska lost to the Italian-American pair of Tathiana Garbin and Meilen Tu.
The Indo-Czech pair was beaten by the Australian-Zimbabwean pair of Paul Hanley and Kevin Ullyett in the Rogers Cup.
Andy Murray suffered his first defeat in nearly three months on Thursday when he was beaten by Latvia's Ernests Gulbis in the third round of the Rogers Cup. Playing just his second match since winning Wimbledon, Murray fell 6-4, 6-3 in less than an hour and a half in one of the key lead-up events to the US Open.
Canadian Milos Raonic declared that he would stop at nothing to win a major title after admitting his straight sets loss to Andy Murray in Sunday's Wimbledon final would sting.
Mahesh Bhupathi and Martin Damm lost 3-6, 6-7 (7-9) against Kevin Ullyett and Wayne Black in the quarterfinals in Montreal
The Indian ace made a shocking exit from the Rogers Cup, losing to Italian qualifier Alberta Brianti.
The 28-year-old Spaniard sustained the injury in practice last month and has been training with a cast on his right wrist, forcing him to miss the Rogers Cup in Toronto and last week's Cincinnati Open.
Czech defending champion Katerina Siniakova fended off Maria Sharapova in a fiercely contested match at the Shenzhen Open on Friday to set up a final with world number one Simona Halep.
Australia's Nick Kyrgios courted more controversy with an off-colour remark to his opponent Stanislas Wawrinka during the second round at the Rogers Cup.
Photos from Day 5 action at the Western & Southern Open at Cincinnati on Thursday.
A summary of the action on Day 3 at the US Open.
Spain's Rafa Nadal handed Novak Djokovic another semi-final defeat when he beat the world number one at the Rogers Cup on Saturday to set up a title decider against local favourite Milos Raonic.
Playing her first match of the North American hard court swing after pulling out of last week's event in Stanford with a sore right elbow, Williams played a ragged opening set in which she was broken four times while firing four double faults.
Robinho came off the bench to head home the winner in Brazil's 2-1 victory over Chile on Tuesday, taking his personal tally to nine against their South American rivals and boosting his chances of playing at next year's World Cup finals.
Maria Sharapova's mix of grit and power were enough to see off American teenager Sofia Kenin 7-5, 6-2 in the third round of the US Open on Friday.
The returning Scot also announced his withdrawal from next week's Rogers Cup in Toronto.
Nick Kyrgios and Bernard Tomic gave Australia an unwanted reputation as a breeding ground for tennis brats during a tempestuous 2015 and the pair will be firmly under the spotlight in front of home crowds at Melbourne Park. With former world number one Lleyton Hewitt set to retire and the last of his two grand slam titles at the 2002 Wimbledon championships a distant memory, Australia has long yearned for a new force in men's tennis to challenge at the majors. Tomic, 23, and Kyrgios, 20, have both been tagged as the future of the sport in the country but the excitement generated by their undeniable talent gave way to dismay last season as the pair hogged the headlines for all the wrong reasons.
Venus Williams got off to a flying start in her return from a two-month layoff but her game quickly fell apart as the seven-time Grand Slam champion slumped to a 0-6, 6-4, 6-2 loss to Kirsten Flipkens in the Rogers Cup first round on Tuesday.
Top seed Serena Williams shook off a spirited attempt by Agnieszka Radwanska and moved into the final of the Rogers Cup with a 7-6(3), 6-4 victory on Saturday and will meet Romania's Sorana Cirstea, whose surprising run continued when she beat China's Li Na 6-1, 7-6(5).
Defending champion Petra Kvitova suffered a shock exit when unseeded Romanian Sorana Cirstea beat the Czech 4-6 7-5 6-2 on Friday to move in the semi-finals of the Rogers Cup.
Roger Federer returned from a month-long layoff with a 6-4, 6-4 second round victory over Roberto Bautista Agut on Tuesday at the Western and Southern Open in Cincinnati.
Stanislas Wawrinka had to dig deep to beat Borna Coric at the Western & Southern Open in Cincinnati on Wednesday and conceded his thoughts had been far from tennis over the past few days.