ISTANBUL, Turkey - No.2 seed Mihaela Buzarnescu was the latest to fall upset bid on Wednesday at the TEB BNP Paribas Istanbul Cup.

On a day in which No.4 seed Dayana Yastremska and No.5 seed Ajla Tomljanovic lost their first-round matches, Russia's Margarita Gasparyan won the last four games to seal a second-round stunner, 1-6, 6-4, 7-5, in the Turkish city.

Read more: Mladenovic serves up Yastremska upset in Istanbul

"I'm a little bit tired, but I'm really happy that I won," Gasparyan said. "For me, every victory is very important, because this year is very special for me. I had injuries, I had surgeries. I recovered from many things, and every victory is very, very important for me."

Gasparyan had led by a break in the final set at 3-2 before the Romanian won four games in a row herself, and found herself two points away from defeat in the ensuing game.

However, Buzarnescu delivered two of her seven double faults for the match in the game in which she served for it, giving the 24-year-old a lifeline in the match as the second came on break point.

The Russian quickly ascended in the match's final games from that point, as she again found herself two points away from defeat on serve in the 10th game, but ran away with the last 10 points of the match to seal the upset in just over two hours.

Ultimately, Buzarnescu won 11 more points than Gasparyan in the match, and had a better break point conversion percentage, but was unable to come away with the victory. 

The Romanian won seven of the nine break points she held, and Gasparyan claimed six of 11, but Buzarnescu's 42 unforced errors to just 28 winners proved to be the key margin that decided the match.

"I was leading 3-1 in the third set, and then she played really well," said the Russian.

"She played really deep and I couldn't receive the ball and did some stupid mistakes. I just relaxed a little bit, I played every point, and I got the result."

A two-time champion at WTA level, Gasparyan was the second player through to the quarterfinals by a matter of minutes on Wednesday, reaching her her first tour-level quarterfinal on clay.

Czech Barbora Strycova also rallied from a break down in the final set to see off another Romanian in Sorana Cirstea, 6-2, 1-6, 6-3, to reach the last eight.