Milos Raonic, who won Sunday's ATP Tour event in San Jose, crashed out in the first round of the US Indoor Championships on Wednesday losing in three sets to wild card Jack Sock.
The 22-year-old Canadian and tournament second seed lost 6-3, 5-7, 7-5 in two hours and 10 minutes to the world number 168 Sock.
Sock advances to the second round where he will face fellow American James Blake.
Sock won the battle of the hard-hitting servers despite having 11 aces to 12 for Raonic. Sock won 83 percent of his first-serve points and saved eight of nine break points.
Raonic dominated Germany's Tommy Haas 6-4, 6-3 in Sunday's final, becoming the first player in more than half a century to win the event three consecutive times.
Former three time Memphis champ Haas defeated Russia's Evgeny Donskoy 7-6 (8/6), 6-4 on Wednesday.
The sixth seeded Haas had six aces and three double faults but won 87 percent of his first-serve points in his first career meeting with Donskoy.
Haas advances to the second round where he will face Feliciano Lopez of Spain.
Former World No. 1 Lleyton Hewitt, a two-time Grand Slam champion, saved two match points on his serve in the 12th game of the second set before defeating Taiwan's Lu Yen-Hsun 2-6, 7-6 (7/3), 6-4 in a first-round match.
Hewitt, 31, is making his third appearance at the $1.58 million hardcourt event, having lost in the 2009 semi-finals and 2011 quarter-finals, both times falling to now-retired US standout Andy Roddick.
New Zealand's Marina Erakovic, who lost to Sofia Arvidsson in last year's Memphis final, avenged that defeat by beating the defending champ 6-1, 3-6, 6-3 in a second-round match.
Also advancing to the women's third round was Belgian top seed Kirsten Flipkens, who eliminated Ukraine's Lesia Tsurenko 7-5, 3-6, 6-3.
British fourth seed Heather Watson defeated Czech Andrea Hlavackova 2-6, 6-0, 6-3 while German third seed Sabine Lisicki eliminated Hungary's Melinda Czink 7-6 (7/0), 4-6, 6-2.