Defending champion Stan Wawrinka was consigned to a shock defeat by Damir Dzumhur before world number one Andy Murray marched into the second round of the Dubai Tennis Championships on Tuesday.
Wawrinka was in tears as he struggled with a knee injury during a thrilling Australian Open semi-final defeat to Roger Federer last month and the US Open champion endured more misery in his first match since losing to his compatriot in Melbourne.
Dzumhur defied the odds to secure the biggest win of his career, ousting the world number three 7-6 (7-4) 6-3 in his first meeting with the three-time grand slam champion from Switzerland.
The Bosnian, ranked 77th, won all three break points he earned against the second seed and fought back from 3-0 down in the first set before going on to win a tie-break.
Outsider Dzumhur surged into a 5-1 lead in the second and an out-of-sorts Wawrinka was unable to avoid an early exit.
Top seed Murray, back in action for the first time since surprise loss to Mischa Zverev in the fourth round of the first major of the year, eased past Malek Jaziri 6-4 6-1.
The Wimbledon champion said he is raring to go in the United Arab Emirates after recovering from a bout of shingles following his return from Australia and responded well to going a break down in the first set to make it through.
Jaziri appeared to be affected by dizziness as he called for a medical timeout at 1-2 and 0-40 down in the second set and it was only a matter of time before Murray booked a second-round encounter with Guillermo Garcia-Lopez.
Qualifier Evgeny Donskoy will face Federer following his 6-4 6-4 win over fellow Russian Mikhail Youzhny, while seventh seed Lucas Pouille was among the other winners on day two of the tournament.