Wildcard Sunil Kumar Sipaeya scripted the biggest upset of the day, shocking second seed Aisam-ul Haq Qureshi of Pakistan in a marathon three-setter to advance to the semi-finals of the US $50,000 SAIL [Get Quote] Open ATP Challenger series tournament in Delhi on Thursday.

In a two-hour battle, the 24-year-old Indian held his nerve to clinch a thrilling 3-6, 7-6(5), 7-6(4) victory over last week's champion and overwhelming favourite and book his maiden last-four berth in a Challenger tournament.

Sipaeya is now up against Czech Republic's Tomas Cakl, who rallied to beat American Alberto Francis 4-6, 6-2, 6-4 in another quarter-final.

"This is certainly one of the big wins for me. This was my first quarter-final at a Challenger event. It was a tense match and the tie-breakers were really close; I am glad to beat a player like him," an elated but exhausted Sipaeya said.

"He serves big and my strategy was to hold serve and take it to the tie-breakers. I guess the tie-breakers were the only hope for me because he is very strong," he added.

It did not seem to be much of a contest when the two players took to the court as Sipaeya is ranked 527 on ATP charts, way below Qureshi, who is 129th at the moment.

In the first set, Qureshi showed just why he was an overwhelming favourite. The 27-year-old literally served out the Indian before breaking him in the eighth game with a well-placed backhand to take the opener in no time.

Perhaps jolted out of his comfort zone, a more determined Sipaeya held serve, saving two break-points, in the second set and cut down on his unforced errors, making Qureshi work hard for every point.

Qureshi, on the other hand, was banking heavily on his powerful serve. The Pakistani number one sent down 13 aces but the lightening fast hits failed to rattle the Indian, who relied on his swiftness on the baseline to earn points.

The second set's tie-breaker was a perfect example of it as Sipaeya engaged Qureshi in long rallies before forcing him to either hit out or bury the returns into the net.

To his credit, Qureshi was brilliant whenever he managed to draw Sipaeya to the net. Except for a few miscued shots, the second seed converted almost all his volleys and drop shots into winners.

But Sipaeya made sure that the match was played to his strengths on the baseline. After clinching the tough second set tie-breaker, the Indian followed the same strategy in the decider, holding serve and frustrating Qureshi in rallies.

Ultimately, the pressure began to show on the Pakistani and his booming first serve began to land invariably on the net.

Qureshi failed to convert a couple of break points that came his way and in the tie-breaker Sipaeya's calm helped him come out trumps.

Meanwhile, in the other quarter-finals, fifth seed Russian Michail Elgin survived a scare from French Sebastian De Chaunac before coming through 4-6, 7-5, 6-4.

Elgin next takes on Ukrainian Ivan Sergeyev, who beat compatriot Ilia Marchenko 6-3, 6-4.

Meanwhile, in the doubles competition, top seeds Patrick Briaud and Alexey Kedriouk were knocked out of the event after the third seeded Chinese pair of Xin-Yuan Yu and Xuan Shao Zeng beat them 6-7(2), 7-6(4), 10-6 in the semi-finals.

Yu and Zeng will now take on Russians Pavel Chekhov and Michail Elgin, who defeated the Austrian-Israeli team of Martin Slanar and Dekel Valtzer 1-6, 6-3, 10-8 in their last four match.

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