Australian Open champion Stanislas Wawrinka suffered a shock defeat to Austrian qualifier Dominic Thiem at the Madrid Masters on Tuesday as his compatriot Roger Federer withdrew to attend the birth of his second set of twins.
A finalist in Madrid last year, Wawrinka seemed on course for a routine win after romping through the first set, but Thiem levelled with some excellent tennis in the second before sealing the biggest win of his career 1-6, 6-2, 6-4 with the only break of serve in the third set.
"I was really positive trying to find a way to win, but I didn't," lamented Wawrinka.
"I had some chances in the third set and I should have played better when I had those opportunities."
Thiem, meanwhile, was surprised himself at the level of play he found in the final two sets to register his first win against a top 10 ranked player.
"I cannot really believe it," said the world number 70.
"I was in this famous zone during the match. I was really unbelievable concentrated."
Wawrinka's defeat means Rafael Nadal is the only top four seed left in the draw before he even starts his campaign on Wednesday as Federer joined Novak Djokovic in withdrawing from the tournament.
Federer announced on Tuesday evening that his wife Mirka had given birth to the couple's second set of twins, this time boys named Leo and Lenny. "Mirka and I are so incredibly happy to share that Leo and Lenny were born this evening! Twins again.. miracle!" Federer wrote on his official Facebook page.
The 17-time Grand Slam champion's withdrawal could benefit Andy Murray as the Scot is now the highest seeded player left in the second quarter of the draw.
Murray will face Nicolas Almagro in his first match at the Caja Magica on Wednesday after the Spaniard needed 11 match points to finally see off Kazakh qualifier Andrey Golubev 6-3, 6-7 (9/11), 7-6 (7/4).
Fifth seed David Ferrer also needed three sets to overcome fellow Spaniard Albert Ramos 7-6 (8/6), 5-7, 6-3, whilst there were also wins for Milos Raonic and the in-form Kei Nishikori.
Thirteenth seed Fabio Fognini raged at umpire Mohamed Lahyani after he was beaten 7-5, 4-6, 6-3 by Ukrainian Alexandr Dolgopolov and 14th seed Tommy Haas also suffered a first round exit at the hands of the Netherlands' Igor Sijsling 3-6, 6-1, 6-4.
There is still plenty of star power on show in the women's Madrid Open as Li Na and Maria Sharapova were victorious.
Sharapova won her first tournament of the season on her return to clay in Stuttgart two weeks ago and looked in fine form as she raced through the first set against American Christina McHale 6-1.
However, McHale went onto take the second 6-4 and led 4-1 in the decider only for Sharapova to respond by reeling off five straight games to set up a meeting with 2011 US Open champion Sam Stosur in the last 16.
The Russian, though, was still far from happy with her overall performance.
"After a really good start I didn't keep that level. I didn't keep doing what I was doing. I think I had a bit of a letdown," she said.
"I didn't create any chances for myself on her serves. I don't think I had a break point at all in that second set and I didn't have a breakpoint until I converted one in the third set.
"I don't feel like I was doing much off of my return and putting any pressure on her and letting her dictate from the first point. That was really getting me in trouble."
Former Wimbledon champion Petra Kvitova was also forced to three sets by American Varvara Lepchenko before advancing 2-6, 6-2, 6-1.
Earlier, Australian Open champion Li had a more simple task as she swept aside fellow Chinese Zheng Jie 6-2, 6-3.
Zheng led the head-to-head record between the two 4-3 before the match, but Li has now won the last four meetings between the pair in straight sets and will face 16th seed Sloane Stephens in the next round.