The Serbian fourth seed was struggling to put away unseeded Shvedova, of Kazakhstan, but chuckled with relief when her tall opponent lined up an easy smash, set herself, but swished at thin air instead of connecting with a ball that was begging to be walloped for a winner.
It was no laughing matter for the 22-year-old Shvedova as it allowed Jankovic to level the set at 4-4 before rolling through the following two games to win 7-5 6-4 and reach her third semi-final at Roland Garros.
"It was nerves and a little bit of wind," said Shvedova, who switched nationality from Russia to Kazakhstan in 2008. "The ball blew and moved a move a little bit. I just missed it. It happens."
Jankovic will have to play better in the last four against Australian Samantha Stosur today. She dropped serve four times in the match and had to rely on her solid baseline play and superior clay court movement to ensure that at least one of the women's top four seeds progressed.