Despite opening her US swing with a win, Serena Williams was concerned with her unforced errors at the Rogers Cup.
Serena Williams said she was her own worst enemy, as she battled to a three-set victory over Flavia Pennetta at the Rogers Cup on Tuesday.
The world number one was a 2-6 6-3 6-0 winner over former number 10 Pennetta, but not before the Italian caused a stir - Williams dropped serve in five of her first six games before arresting her set-and-a-break deficit.
The American gave credit to Pennetta, not before lamenting her own performance in what was her first match of the US swing - her last could very well be a Grand Slam-sealing win at the US Open.
"Unforced errors pretty much. I had a lot of unforced errors," Williams replied, when asked what went wrong in the first set.
"I just told myself to drop it, like drop the racquet low and get ready to do everything I could to get into the game and to try to do different things, and that's what I started doing out there.
"I was thinking, 'The last time I was here I won [in 2013]. I should at least try to get through this and give 200 per cent, and I started playing better. I was still making errors, but I just started playing better and making less errors.
"But she played really well today - she was hitting deep and doing a lot of things so well."
Williams also put her rusty start down to a lack of matches on hard courts, having last appeared competitively on the surface in March in her Miami Open title.
"It was a good opportunity for me because I hadn't played a match on hardcourts since April-ish, early, early April, after Miami. It was a long time ago," she added.