Maria Sharapova's Wimbledon return ended in defeat as she blew a vast lead to crash out against fellow Russian Vitalia Diatchenko.
The 31-year-old was making her first appearance at the All England Club in three years having served a doping ban and then withdrawn from qualifying through injury 12 months ago.
It was also her first appearance on grass in that time, having pulled out of competing in Birmingham last month.
The 2004 Wimbledon champion won the first set on a tie-break and was soon a game away in the second - leading 5-2 - from a smooth passage into round two.
But Diatchenko broke back, took the ensuing tie-break and prevailed in the third to win 6-7 (3/7) 7-6 (7/3) 6-4 and reach round two.
After Sharapova secured a break of serve in the first set, Diatchenko needed a medical time-out for what appeared to be a hip injury.
Yet the world number 132 did not seem in too much discomfort as she promptly broke straight back for 4-4.
Sharapova was too strong in the tie-break and converted the first of three match points with an ace.
A solitary break at the start of the second looked like proving decisive until Sharapova was pegged back again, and this time Diatchenko made it count.
Again Sharapova broke early in the decider, and again Diatchenko hit straight back. Then, serving to stay in the match, Sharapova bowed out limply with a 10th double fault on match point sealing her fate.
Garbine Muguruza's defence of her Wimbledon title got off to a winning start as she fended off Naomi Broady.
The Spaniard was the queen of Centre Court in 2017, beating Venus Williams in the final, and she enjoyed her return there with a 6-2 7-5 success over the British number four.
She made slightly hard work of it in the second set, but eventually got the job done in an hour and 30 minutes.
Two breaks of serve were enough as Muguruza barely broke sweat in the opening set, with Broady unable to match her precision.
The Stockport player, once Britain's number two, showed resistance in the second set as she was determined to extend her stay on the main show court.
But there was a sense of inevitability about Muguruza breaking at 6-5, and she did to love, as she booked her place in the second round.
The 24-year-old Muguruza was happy to return to Centre Court and said: "It was incredible, it is a beautiful court, I am back and it is always good, I wanted to win and enjoy it more.
"I am happy with my serve and controlling the emotions, to be back in a grand slam is always emotional so I am happy the way I am playing.
"I knew she had a big serve and big shots and on grass it's always difficult."
Upset of the Tournament so far?
— Wimbledon (@Wimbledon) July 3, 2018
Aliaksandra Sasnovich stuns Petra Kvitova in the first round, winning 6-4, 4-6, 6-0#Wimbledon pic.twitter.com/5u6PrQWIlE
World number one Simona Halep saw off Kurumi Nara 6-2 6-4.
The Romanian was playing her first match since winning the French Open last month - her maiden grand slam.
And she looked like a possible candidate to add a second major title, completely bossing her encounter with the Japanese on Centre Court.
Pre-tournament favourite Petra Kvitova was stunningly dumped out by Aliaksandra Sasnovich (below).
The two-time champion was second best on Court One and went down to a 6-4 4-6 6-0 loss.
Kvitova was the bookmakers' tip for a third crown here after winning in Birmingham a fortnight ago.
The Czech then withdrew midway through the Nature Valley International at Eastbourne last week in order to protect a hamstring niggle, but the injury appeared to play no part in the defeat.
British number one Johanna Konta was made to work hard for a 7-5 7-6(7) victory over Russian youngster Natalia Vikhlyantseva.
Konta last year became the first British woman to reach the Wimbledon semi-finals since 1978.
"First rounds are always tricky," she said. "Both players are trying to find their footing.
"I'm playing this championship independent of what happened last year. Last year gave me memories and valuable experience, but I'm older and a little wiser."
Konta faces Dominika Cibulkova next.
Cibulkova (above) put her seeding disappointment behind her by beating Alize Cornet.
The Slovakian is ranked 32 in the world, usually enough to be seeded at a grand slam, but missed out due to Wimbledon's decision to hand a seed to Serena Williams.
She strongly contested the decision but let her tennis do the talking against the Frenchwoman, winning 7-6 (7/4) 6-1.
Bidding to become just the sixth woman in the Open Era to successfully defend the #Wimbledon title...@GarbiMuguruza is through to the second round with a 6-2, 7-5 win over Naomi Broady pic.twitter.com/nofth88pa9
— Wimbledon (@Wimbledon) July 3, 2018
Angelique Kerber got her campaign off to the best possible start with a straights-sets win over Vera Zvonareva.
The German, a 2016 finalist and former world number one, beat the Russian 7-5 6-3.
Kerber (below) was a semi-finalist at Eastbourne last week and will be targeting another deep run at the All England Club.
Gabi Taylor put up a brave fight but her maiden senior Wimbledon outing ended in a three-set defeat to Eugenie Bouchard.
The 20-year-old, who was handed a wild card into the main draw, was beaten 6-0 4-6 6-3 by the 2014 finalist.
Taylor hit the headlines in 2016 when she thought she had been poisoned after having to pull out of the girls' quarter-finals, but it was later confirmed to be a virus.
She did not win a game in the first set, but battled back to take the second before Bouchard's quality told.
Simona Halep, the newest member of the Grand Slam champions' club, silenced a roaring Japanese army of supporters as she demolished Kurumi Nara 6-2 6-4 "on the most beautiful court in the world" to reach the second round.
Playing with a lighter load on her shoulders after winning the French Open title last month, Halep rolled back her arms and let the winners fly off her racket strings.
"I was relaxed when I came here. I didn't push myself. I didn't put pressure on myself. I felt ready today," Halep said with a smile after winning her first match as a major champion.
"I have expectations for myself, but not with the result. I feel ready to fight."
Britain's Heather Watson lost 6-4 7-5 to Belgian Kirsten Flipkens.
