ST. PETERSBURG, Russia - Eighteen-year-old Russian qualifier Elena Rybakina pulled off a stunning victory at the St. Petersburg Ladies' Trophy on Wednesday afternoon, saving a match point to defeat No.3 seed Caroline Garcia and move through to her first WTA quarterfinal, 4-6, 7-6(6), 7-6(5).

Rybakina defeated Timea Bacsinszky in the first round in the Swiss' first match of 2018 as she returns from a hand injury for her first WTA main draw victory, showed tennis well above her ranking of World No.450 for the duration of Wednesday's nearly two-and-a-half hour encounter - her first against a Top 10 player.

Rybakina came from a break down twice in the second set to reach a tiebreak, and pulled off an improbable comeback to take the World No.7 the distance before Garcia pulled off a comeback of her own to force a dramatic, winner-take-all conclusion.

"I was really nervous [towards the end], took more risk. I knew that I need to do it, otherwise I couldn’t win it," Rybakina said.

"There were some mistakes, but I was ready that something could going wrong, because I played against a top opponent. I’m happy that I could continue and win it."

Trailing 4-0 in the second set tiebreak, the teenager won five points in a row to get back in it, and later saved a match point on her serve at 6-5, before she came all the way back to force a decider.

With momentum firmly on her side, the 18-year-old earned what looked to be the decisive break in the fifth game, and nearly held on despite stern resistnace from the Frenchwoman's side of the court.

Serving for the match at 5-4, Rybakina struck a pair of forehand winners to move just two points away from the biggest victory of her career, but was pegged back even and needed a strong service game to stay in the match and force a tiebreak.

The teenager twice led by a mini-break in the tiebreak, but needed to summon all her nerve to win the final two points, claiming victory in two hours, 27 minutes.

Rybakina broke Garcia in her first service game in each set to make a dream start in front of her home fans, but proved unable to hang on to her momentum as the No.3 seed moved ahead late.

The Russian handed her advantage back in the very next game on each occasion, and the two players remained even until Garcia raised her level late in each set.

Garcia broke serve a second time in the seventh game of the first set, the lone game on the teenager's serve which went to deuce in the opener, and held on to her lead from there en route to taking a one-set lead.

It was the Frenchwoman's clean tennis which proved the difference-maker in the first set, as she struck just three unforced errors to 13 from the teenager over the first 10 games.

The second set looked as though it was headed for more of the same as the No.3 seed secured what looked to be the decisive break in the ninth game to serve for the match, but Rybakina had other ideas with her back firmly against the wall.

With clean, precise hitting off the ground - capped with a backhand winner - the 18-year-old broke Garcia's serve to stay in the match, and later forced the World No.7 to serve her way into a tiebreak.

Once there, Rybakina erased her slow start in the blink of an eye, as she cleaned lines off the ground and on serve to send the match into a decider despite a difference of over 400 spots in the rankings between the two players.

The second set proved to be an inverse of the first in more ways than one - though both players hit 14 unforced errors in the set, it was the teenager's flurry of winners, 15 in total, which nearly doubled Garcia's total of eight.

The Russian, making her 2018 season and tournament debut in St. Petersburg, will face the winner of the match between No.5 seed Julia Goerges and Roberta Vinci in the last eight.