Borna Coric made a first-round exit at the Miami Open as Andreas Seppi cruised on Thursday.
Coric, the world number 46, went down to Denis Istomin in a huge battle at the ATP 1000 event.
Joining Istomin in progressing was Andreas Seppi, the Italian crushing American left-hander Donald Young.
Other winners included Adrian Mannarino, Aljaz Bedene, John Millman and Federico Delbonis.
CORIC EXITS, YOUNG THRASHED
Coric was expected to set up a meeting with Andy Murray - a player he beat in Dubai last year - but the Croatian teenager suffered a 4-6 7-5 7-5 loss to Istomin.
Seppi needed just over an hour to thrash Young 6-3 6-1 in a one-sided affair.
Delbonis, who beat Murray at Indian Wells, remains on track for another meeting with the Brit after getting past wildcard Elias Ymer 6-1 4-6 6-3.
ISTOMIN PUNISHES CORIC
Coric served for the match against Istomin during the second set. However, from 5-5, the Uzbek won eight of 10 points.
The win was Istomin's first on the ATP World Tour this season.
Mannarino only lost one point on his serve in the second set of his 2-6 6-2 6-3 win over Illya Marchenko.
FEDERER SET FOR DEL POTRO
Federer, making his return from injury, faces Juan Martin del Potro in the second round.
"We're both in a similar situation," the Swiss 17-time grand-slam champion said. "His injury was much, much greater.
"That's why I'm really pleased for him that he was able to find a way back onto the tour."
DJOKOVIC BEGINS CAMPAIGN
Federer and Del Potro will take centre stage as they meet for the first time since 2013. It is a repeat of the 2009 US Open final, won by the Argentinian for his only grand slam. Novak Djokovic opens his Miami campaign against Kyle Edmund, while David Ferrer and Tomas Berdych are also in action.