Miami - Canadian Vasek Pospisil spoiled Juan Martin del Potro's return from injury on Thursday with a 6-4, 7-6 (9/7) first-round win over the former US Open champion in Miami.
Argentina's del Potro, a clear fan favorite, showed the rust after months of left wrist injury rehab in a contest lasting a shade under two hours.
The former world number four, who has slumped to 616 in the rankings, double-faulted on a set point which would have levelled the contest at a set each. Moments later he saved a match point with an ace, but finally succumbed with a service return long.
Del Potro, who had come back from right wrist surgery in 2010, underwent surgery on his left wrist last March.
He finished the 2014 season outside the top 100 for the first time since 2005 after contesting just four tournaments during the year.
Del Potro made an aborted comeback attempt in January before pulling out of the Australian Open because of pain in the wrist and underwent a second surgery two months ago.
He turned down a wild card into this month's hard-court tournament in Indian Wells, California, before declaring himself ready for the combined WTA and ATP Masters hard-court tournament here.
"I don't feel frustrated, I have to take the positive things on my comeback," del Potro said. "It doesn't matter the score for now. Obviously I wanted to win the match, and I had few chances in the first set, then in the second set.
"I didn't serve well in the special moments, which is tough for me with all of these things. Nut now I'm OK. I don't have any physical problem after the match, and I will be recovering soon for the future."
Pospisil, 24 and ranked 60th in the world, fired 35 winners, converting two of his three break opportunities. Del Potro, who hit 25 unforced errors, managed to convert just one of his break point chances.
But after a rehabilitation process that tested his patience and determination, del Potro said even a bumpy return to competition is a pleasure.
"Mentally you must be strong enough to deal with the problem and get up every morning to do your treatments and rehab and stay calm, looking forward for the future," he said. "I'm not hurried to be in the top 10 very soon. I want to play tennis. It doesn't matter how long it takes me to be in the top again.
"I just wanted to play tennis and without pain."
In other first-round ATP matches on Thursday, a pair of young guns advanced as German Alexander Zverev defeated Australian Sam Groth 7-5, 6-7 (5/7), 6-4 and Croatia's Borna Coric rallied to eliminate Austrian Andreas Haider-Maurer 1-6, 6-3, 7-6 (7/3).
In women's play, seventh seed Agnieszka Radwanska of Poland advanced to the third round with a tough 6-4, 7-5 win over Slovakian Anna Schmiedlova while German ninth seed Andrea Petkovic advanced past American Christina McHale 6-2, 6-2.
"I was in trouble, especially in that second set," said Radwanska. "But what was most important is that I was really playing good shots in the really key points, in the break points.
"I'm very glad that I could finish in two sets," she said.
Spanish 12th seed Carla Suarez Navarro beat Swiss Stephanie Voegele 6-3, 6-1, Czech 14th seed Karolina Pliskova defeated Annika Beck of Germany 2-6, 6-3, 6-4.
The French pair of Kristina Mladenovic and Alize Cornet both won, with Mladenovic beating Barbora Zahlavova Strycova 7-5, 6-2 and Cornet beating Russian Elena Vesnina 6-4, 6-1.Results on Thursday from the third day of the ATP and WTA Miami Open (x denotes seeded player):
Agnieszka Radwanska (POL x7) bt Anna Schmiedlova (SVK) 6-4, 7-5
Irina Begu (ROM x31) bt Tereza Smitkova (CZE) 5-7, 6-4, 6-4
Alize Cornet (FRA x22) bt Elena Vesnina (RUS) 6-4, 6-1
Carla Suarez Navarro (ESP x12) bt Stephanie Voegele (SUI) 6-3, 6-1
Venus Williams (USA x16) bt Urszula Radwanska (POL) 6-3, 6-2
Samantha Stosur (AUS x23) bt Pauline Parmentier (FRA) 6-1, 3-6, 6-0
Kaia Kanepi (EST) bt Varvara Lepchenko (USA x28) 6-2, 6-4
Caroline Wozniacki (DEN x4) bt Madison Brengle (USA) 6-0, 6-1
Ekaterina Makarova (RUS x8) bt Karin Knapp (ITA) 6-1, 6-3
Elina Svitolina (UKR x26) bt Bojana Jovanovski (SRB) 6-3, 7-6 (7/3)
Kristina Mladenovic (FRA) bt Barbora Zahlavova Strycova (CZE x19) 7-5, 6-2
Andrea Petkovic (GER x9) bt Christina McHale (USA) 6-2, 6-2
Karolina Pliskova (CZE x14) bt Annika Beck (GER) 2-6, 6-3, 6-4
Paula Badosa Gibert (ESP) bt Zheng Saisai (CHN) 6-1, 7-5
Kurumi Nara (JPN) bt Caroline Garcia (FRA x25) 6-3, 7-6 (11/9)
Daria Gavrilova (RUS) bt Maria Sharapova (RUS x2) 7-6 (7/4), 6-3
Martin Klizan (SVK) bt Paolo Lorenzi (ITA) 6-3, 6-4
Steve Darcis (BEL) bt Malek Jaziri (TUN) 2-6, 7-5, 7-5
Thomaz Bellucci (BRA) bt Lleyton Hewitt (AUS) 7-5, 6-7 (2/7), 6-4
Alexandr Dolgopolov (UKR) bt Ricardas Berankis (LTU) 6-4, 6-1
Mikhail Kukushkin (KAZ) bt Steve Johnson (USA) 6-4, 3-6, 6-2
Alejandro Falla (COL) bt Michael Berrer (GER) 6-7 (5/7), 6-4, 6-4
Federico Del Bonis (ARG) bt Jir Vesely (CZE) 7-6 (7/4), 3-6, 7-5
Alexander Zverev (GER) bt Sam Groth (AUS) 7-5, 6-7 (5/7), 6-4
Mikhail Youzhny (RUS) bt Andrey Golubev (KAZ) 4-6, 6-2, 6-3
Simone Bolelli (ITA) bt Marcos Baghdatis (CYP) 6-2, 6-2
Borna Coric (CRO) bt Andreas Haider-Maurer (AUT) 1-6, 6-3, 7-6 (7/3)
Jerzy Janowicz (POL) bt Edouard Roger-Vasselin (FRA) 6-4, 6-2
Vasek Pospisil (CAN) bt Juan Martin del Potro (ARG) 6-4, 7-6 (9/7)
Andrey Rublev (RUS) bt Pablo Carreno-Busta (ESP) 1-6, 6-1, 6-4
Jurgen Melzer (AUT) bt Ryan Harrison (USA) 7-6 (7/3), 6-3
Teimuraz Gabashvili (RUS) bt Pablo Andujar (ESP) 0-6, 7-6 (7/4), 6-3