First day of the US Open Men 2015, saw a record breaking 6 retirements in round 1.
Interestingly, all matches had passed the first set hallmark and match betting will stand at many bookmakers. One of the 6 retirements was Yen-Hsen Lu, who was tipped (Lu Injury) as a potential retirement heading in his first round match.

Illya Marchenko (Ukraine) beat 16-Gael Monfils (France)

2-6 6-4 5-0 (Monfils retired)

Samuel Groth (Australia) beat Alexandr Dolgopolov (Ukraine)

4-6 6-1 7-5 (Dolgopolov retired)

Teymuraz Gabashvili (Russia) beat Pablo Andujar (Spain)

7-6(6) 0-6 4-6 6-4 0-0 (Andujar retired)

Martin Klizan (Slovakia) beat Florian Mayer (Germany)

6-7(5) 6-3 6-3 3-0 (Mayer retired)

Marsel Ilhan (Turkey) beat Radek Stepanek (Czech Republic)

6-0 2-6 6-4 3-2 (Stepanek retired)

Mikhail Kukushkin (Kazakhstan) beat Lu Yen-Hsun (Taiwan)

6-3 6-3 3-0 (Lu Y H retired)