Many of the world's top tennis players paid their respects to former ATP chairman Brad Drewett on Sunday with a minute's silence at the Madrid Open.
Australian Drewett died aged 54
after battling motor neurone disease.
Novak Djokovic, Serena Williams and Andy Murray were among those to wear ribboned badges and gather in the Manolo Santana stadium for Drewett.
When play got under way, Serena Williams won but 10th seed Caroline Wozniacki and fifth seed Li Na lost.
World number one and defending champion Williams opened her European clay-court campaign with a 7-6 (7-5) 6-1 win over Kazakhstan's Yulia Putintseva, the world number 88.
"I felt a little sluggish out there, but I'm happy I was able to win the match," said Williams.
"I obviously have to and want to play better as each match goes on."
Wozniacki earlier lost 6-2 6-4 to Yaroslava Shvedova, and American Madison Keys beat former French Open champion Li 6-3 6-2.
Polish fourth seed Agnieszka Radwanska beat Tsvetana Pironkova of Bulgaria 6-2 6-4 and will meet
Briton Laura Robson
in round two.
Venus Williams was forced to withdraw from the event because of a back injury, but her sister did enough to set up a second-round match against Lourdes Dominguez Lino.
Maria Sharapova is the second seed in Madrid and will begin her campaign on Monday, while Djokovic, Murray, Roger Federer and Rafael Nadal are all in the men's draw.
Asked for his thoughts on the passing of Drewett, world number one
Djokovic told the ATP:
"It's very sad. My condolences to his family. It's devastating news for not just us tennis players, but the tennis world."
Federer added: "Obviously Brad wasn't just the president of the ATP but was a player himself, a board member. He's given so much time and effort to the ATP, and I think this is really what we will try to honour in a small way today."
The Madrid tournament has reverted to using traditional red clay courts this year, after an experiment with blue clay led to the likes of Nadal and Djokovic threatening a boycott in future.
"I think that obviously the court last year was not up to the level that we needed," said Nadal. "It was not prepared to be a competitive court, but the courts are impressive this year.
"In Madrid, we have the problem of the dry climate, so it's very difficult to have the clay that settles down properly, a clay that's the same as in other places. I think this year we have managed to have good clay here."
won his first title since 2011 as he upset top seed David Ferrer 6-1 6-4 to win the Portugal Open, and
beat compatriot Philipp Kohlschreiber 6-3 7-6 to win the Munich Open.