Stosur has always had trouble with Vesnina - she had lost two of their three previous meetings, and in her only win barely escaped in three sets. This time was no different - after finishing the first set off in 38 minutes with a huge forehand winner, she found herself serving at 0-3, 0-30 in the second set.
But Stosur has been doing a lot of winning lately and that may have been what helped her turn it around so quickly - the No.4-seeded Australian ran off six games in a row from there, and 24 of the next 33 points, to end it. The No.5-seeded Vesnina netted a crosscourt backhand on match point.
"The start was definitely quite close," Stosur said afterwards. "We both had a few opportunities on each other's serve at the start, and then at 4-3 I think she had 40-15 up and made a couple of errors, and all of a sudden it was deuce and there was a little bit more pressure on her. I managed to return quite well from there and get that break, then served it out. I think that was the main difference in that first set.
"Second set, my level probably went a little bit down and hers a little bit up, and I found myself 3-0 down pretty quickly. But I regrouped and was able to play well again, and won those last six games.
"It was important to bounce back as quickly as possible so she couldn't get a real run going."
After somewhat of a slump in August and September - she was just 6-5 in five tournaments - Stosur is now a sparkling 10-1 since the start of October, a stretch that includes winning the Osaka title, reaching the final of Moscow (falling to Simona Halep) and now winning her opening match here in Sofia.
"Anytime you win a group of matches like that it makes you feel good, and maybe in those tough moments in the matches you're in, you can draw on some of that confidence and think, 'I can do better, I can do this, I can hit that shot,' because you've been doing it day in and day out the last few weeks.
"So having a run of matches can certainly build confidence and help you in each match."