Four-time Grand Slam champion Naomi Osaka crashed out of the Madrid Open in the first round on Tuesday with a 6-4, 2-6, 6-4 defeat by Lucia Bronzetti.
The Japanese former world No 1, ranked 55th, battled back with a strong second set after losing the first, but eventually came up short against her determined Italian opponent.
"From the outside maybe it seems easy but when you're on the court against a great champion like her it's always difficult – I'm proud with how I managed the match," said Bronzetti.
"She hit the ball very strong... I tried to make some variation in my game like drop shot, I got a lot of points with that."
Osaka, who is still finding form after a 15-month break from tennis and last played at the Miami Open in March, secured two break points in the fourth game of the first set which she spurned.
Bronzetti broke in the seventh and served it out, before Osaka responded strongly.
The 27-year-old secured three breaks of serve and conceded one to force a decider.
Osaka immediately conceded a break and despite wrestling back on serve at 3-3 when she took her fifth break point of the game, was broken herself again straight away.
Bronzetti triumphed when Osaka slipped as she tried to reach a cross-court shot.
The Italian will face American world No 5 Madison Keys in the second round.
"I played against her two times, it's going to be a real tough match like today," said Bronzetti.