In a career that has generated 54 singles titles, including 16 Grand Slams, Williams has won just about everything there is to win in her sport but Cincinnati, one of the WTA Tour's most prestigious tournaments, is not on that very long list.
If the world number one is to add a 55th title to her haul here she will have to perform at a much higher level than she did against the plucky but overmatched 19-year-old Canadian.
"Every ball I hit seemed to be going out and I even had the easiest approach shot and it went not slightly wide, it was like 50 feet out," said Williams, who was playing in her first match since Sunday's crushing win over Sorana Cirstea in the Toronto final.
"That was actually embarrassing.
"I thought I'd never hit a shot like that professionally. I have maybe in practice with my eyes closed but never conscious have I hit a shot like that.
"So it was just some crazy tennis out there."
Staring across the net at a number one ranked opponent for the first time, Bouchard registered an early shock when she broke Williams to open the match and held serve to go up 2-0.
Williams, who has already matched a career high this season winning eight titles, won the next two games but Bouchard would not back down breaking her opponent a second time on way to taking the first set.
In the second set, the powerful Williams would begin to show her class registering the early break to take the set and level the match then doing just enough in the third to finish off the 62nd ranked Bouchard.
Despite piling up 49 unforced errors, more than double the 23 from Bouchard, Williams still had enough weapons, including seven aces, to get the job done and run her match record this season to a stellar 57-3.
Italian sixth seed Sara Errani and her 12th seeded compatriot Roberta Vinci both advanced to the third round with testing three set wins.
Errani outlasted Slovenian qualifier Polona Hercog 6-4 5-7 6-4 while Vinci was a 6-4 6-7 (3) 6-3 winner over Germany's Andrea Petkovic.
Australian 11th seed Samantha Stosur, the 2011 US Open winner, had smoother passage taming American Jamie Hampton 6-3 7-6 (3).
Cincinnati Open results
5-Li Na (China) beat Lauren Davis (U.S.) 4-6 6-1 6-1
Simona Halep (Romania) beat 8-Marion Bartoli (France) 3-6 6-4 6-1
4-Agnieszka Radwanska (Poland) beat Varvara Lepchenko (U.S.) 6-4 6-0
Magdalena Rybarikova (Slovakia) beat Alize Cornet (France) 3-6 7-5 7-5
10-Caroline Wozniacki (Denmark) beat Monica Niculescu (Romania) 6-4 6-3
14-Jelena Jankovic (Serbia) beat Ekaterina Makarova (Russia) 2-6 6-3 6-3
Elena Vesnina (Russia) beat Venus Williams (U.S.) 6-2 5-7 6-2
7-Petra Kvitova (Czech Republic) beat Marina Erakovic (New Zealand) 6-4 6-7(7) 6-3
9-Angelique Kerber (Germany) beat Alisa Kleybanova (Russia) 7-6(3) 6-2
Mona Barthel (Germany) beat 16-Maria Kirilenko (Russia) 6-4 6-4
1-Serena Williams (U.S.) beat Eugenie Bouchard (Canada) 4-6 6-2 6-2
12-Roberta Vinci (Italy) beat Andrea Petkovic (Germany) 6-4 6-7(3) 6-3
6-Sara Errani (Italy) beat Polona Hercog (Slovenia) 6-4 5-7 6-4
11-Samantha Stosur (Australia) beat Jamie Hampton (U.S.) 6-3 7-6(3)