Sam Querrey safely reached the last 16 of the BB&T Atlanta Open but two American hopefuls failed to qualify for the first round.
Croatian wildcard Borna Coric impressed with a straight-sets victory over seventh seed Edouard Roger-Vasselin to reach the second round of the Croatian Open.
Serbian wildcard Viktor Troicki saw off eighth seed Dominic Thiem to claim a shock first-round win at the Credit Agricole Swiss Open on Monday.
Fifth seed Bojana Jovanovski survived a scare before coming through her Baku Cup first-round match against Patricia Mayr-Achleitner.
Wildcard Bernard Tomic almost fluffed his lines but ultimately managed to dethrone Ivo Karlovic and clinch the Claro Open Colombia title.
Leonardo Mayer came from behind to upset the odds and beat top seed David Ferrer to win the bet-at-home Open final in Hamburg.
Top seed Caroline Wozniacki proved far too strong for Roberta Vinci as the Dane powered to a simple straight-sets victory to claim the Istanbul Cup.
Mona Barthel picked up her third WTA title as the pre-final favourite beat Chanelle Scheepers to win the Swedish Open title in straight sets.
Top seeds Caroline Wozniacki and Roberta Vinci will meet in the final of the Istanbul Cup after both women registered routine semi-final victories.
David Ferrer and Leonardo Mayer will contest Sunday's bet-at-home Open final in Hamburg after winning their respective semi-finals on Saturday.
Ivo Karlovic remains on course to retain his Claro Open Colombia title after beating Radek Stepanek to reach this year's final in Bogota.
Germany's Mona Barthel and South Africa's Chanelle Scheepers will play for the Swedish Open title in Bastad after winning their semi-final matches on Saturday.
Caroline Wozniacki battled to a three-set win over Karolina Pliskova to reach the semi-finals of the Istanbul Cup.
Top seed Richard Gasquet crashed out of the Claro Open Colombia in Bogota on Friday, losing his quarter-final match 6-3 6-4 against Dominican Republic's Victor Estrella Burgos.
Alexander Zverev's dream week continued as the German teenager recovered from a bad start to defeat Tobias Kamke in the quarter-finals of the bet-at-home Open in Hamburg.