Second seed Hyeon Chung frittered away a handsome lead to suffer a shock exit from the Tata Open Maharashtra while top seed Kevin Anderson and defending champion Gilles Simon had to dig deep to beat their respective opponents here on Wednesday.
Latvian Ernests Gulbis erased a 0-4 deficit to knock out World No 25 from South Korea 7-6 (2), 6-2 in the second round.
"I think I started slow and he (Chung) was much better in the first set but I managed to comeback to save the set from 2-5 down and the rhythm helped me in saving the match," said a delighted Gulbis after the match.
Chung was not pleased with his performance. "I thought I had a good start in the first set but I started to lose points and it became tough to comeback but I will need to improve in the coming season and hope to come back here next year."
Later, South African Anderson had to give his all before prevailing 7-6 (2), 7-6 (6) over Serbia's Laslo Djere in two hours and eight minutes.
Anderson will now fight it out with seventh seed Jaume Munar, who sent packing qualifier Simone Bolleli 7-5, 6-0.
Ranked 93, Illya Ivashka of Belarus stretched World No 30 Simon, who had to grind his way to quarterfinals with a 6-7 (3), 6-2, 6-1 after battling hard for two hours and 31 minutes.
Third seed Simon, who usually has effortless movement, had to run a lot on court with Ivashka returning almost everything.
Also advancing to the quarterfinals was fifth seed Benoit Paire, who defeated Cez Jiri Vesley 6-4, 6-2.
Steve Darcis's impressive comeback was extended to quarterfinals with a 4-6, 7-6 (4), 6-2 win over talented American youngster Michael Mmoh.