Teenager Borna Coric produced a performance beyond his years to stun Andy Murray at the Dubai Tennis Championships.
Victoria Azarenka remains unstoppable at the Qatar Total Open, after adding Caroline Wozniacki to her list of scalps.
Rafael Nadal needed just 64 minutes to book his spot in the Argentina Open quarter-finals.
Defending champion Grigor Dimitrov suffered a shock defeat to Ryan Harrison in the second round of the Abierto Mexicano Telcel.
Andy Murray made short work of Joao Sousa once again to race into the quarter-finals of the Dubai Championships.
Kei Nishikori survived a second set scare before booking his place in the second round of the Abierto Mexicano Telcel.
Seeded trio Jiri Vesely, Pablo Andujar and Pablo Carreno Busta all fell at the first hurdle of the Argentina Open.
Venus Williams was the first player to advance to the last eight of the Qatar Total Open.
Novak Djokovic secured a straight sets win over Vasek Pospisil in the first round of the Dubai Duty Free Championship.
Andy Murray moved into the second round of the Dubai Championships with a straight-sets win over Gilles Muller.