Steve Johnson's impressive run at the Citi Open in Washington came to an end at the quarter-final stage as he was beaten by second seed Milos Raonic on Friday.
Angelique Kerber and Varvara Lepchenko were similarly clinical in securing their semi-finals berths at the Bank of the West Classic in Stanford, each needing less than an hour to claim respective victories over Garbine Muguruza and Sachia Vickery.
The seemingly unstoppable David Goffin reached his first ever ATP World Tour final after overcoming Maximo Gonzalez in the semi-finals of the bet-at-home Cup Kitzbuhel.
Rafael Nadal's US Open participation has been called into question by an injury which will force him to wear a cast on his right wrist for up to three weeks.
Steve Johnson claimed another notable scalp at the Citi Open in Washington after downing ninth seed Ivo Karlovic to reach the quarter-finals.
Third seed Angelique Kerber survived a major scare to progress through to the quarter-finals of the Bank of the West Classic in Stanford at the expense of Coco Vandeweghe.
Third seed Lukas Rosol's hopes of second career title were ended when he suffered a quarter-final defeat to qualifier Maximo Gonzalez at the bet-at-home Cup Kitzbuhel.
Top seed Tomas Berdych lived up to his billing in the second round of the Citi Open in Washington with a straightforward win over qualifier Robby Ginepri.
Serena Williams enjoyed an overdue taste of victory as she beat Karolina Pliskova in her opening match at the Bank of the West Classic in Stanford on Wednesday night.
Lukas Rosol safely made it through to the quarter-finals of the bet-at-home Cup Kitzbuhel on a rain-interrupted day's play in Austria.
Kevin Anderson became the first man through to the third round of the Citi Open after a straightforward victory over Evgeny Donskoy in Washington DC.
Fifth seed Ana Ivanovic overcame Germany's Sabine Lisicki in straight sets to move into the second round of the Bank of the West Classic in Stanford.
Sixth seed Robin Haase suffered a shock first-round defeat to Paolo Lorenzi at the bet-at-home Cup Kitzbuhel.
American Robby Ginepri will face top seed Tomas Berdych in the second round of the Citi Open after winning his opening match against Alejandro Falla in Washington DC.
Karolina Pliskova booked a second-round encounter against world number one Serena Williams by beating Japan's Kimiko Date-Krumm in the first round of the Bank of the West Classic in Stanford.