On a day when four seeds tumbled, top seed Karan Rastogi [Images] and giant killer Treta Bhattacharya moved into semi-finals after epic battles at the National Grasscourts Championships in Kolkata on Thursday.

The seeds, who were shown the door, were men's second seed Ashutosh Singh and women's second seed Sonal Phadke, third seed Asha Nand Kumar and sixth seed Ragini Vimal.

In the first match of the day and perhaps the best match of the tournament so far, Rastogi defeated comeback man Mankad in a tough three-setter that was far more competitive than what the result 6-4 4-6 6-3 showed.

If Mankad dished out the big serves, Rastogi replied with clinical returns.

As Mankad opted for a chip and charge game, Rastogi secured more points with his passing shots as he left the court more exposed.

Rastogi took the first set with breaks in the 8th and 10th games after being broken in the very first service game.

In the second set, Mankad showed his stomach for a fightback and broke Rastogi in the first and 7th games and looked to be crusing for the set.

But Rastogi created a break in the eighth game, setting up the point with a back-hand return and then setting up the break point with a back-hand down the line that left Mankad stranded.

However, Mankad held serve in the next service game to level scores.

The third set saw, Rastogi collect an early break in the second game, but Mankad rallied to level scores in the fifth game. However, two unforced errors from the baseline handed Rastogi a vital break in the very next game and he held serve to clinch the affair.

After the match, Mankad said, '' It is great to comeback and play three matches in three days. I am planning on my rehab and competitive tennis and hope to carry on without much problem.''

In the other big tie of the day Treta had a humdinger of a game, overcoming her senior pro Ragini Vimal in a three setter 6-4 5-7 6-4 in two hours seven minutes.

Ragini Vimal, seeded sixth in the championship, was surprised by the sharp returns and court presence of the 16-year old.

The fortunes of the two fluctuated as both the players slugged it out from the baseline. Treta took the first set with breaks in 2nd, 6th and 10th game, and was broken in the third and seventh games.

In the second set Vimal came back with vengeance taking the set 7-5, with breaks in the 1st, 3rd, 5th and 11th games. She was broken in the 2nd, 4th and 10th games as the slugfest continued between the duo.

The third set saw Vimal tiring and that gave Treta the advantage as she dictated the terms from the baseline, making Vimal run from corner to corner.

She effected four breaks after being broken in the 1st, 5th and 9th games.

Treta broke in the 4th, 6th, 8th and 10th games as Vimal failed to hold any of her last four service games to concede the match.

After the match Treta said, '' I am very excited and happy. This is my first senior Nationals and to have gone so far is an achievement. I didn't expect to reach this big. But I am focussed and taking one match at a time.''

Second seed Ashutosh, carrying an ankle tendonitis, conceded his match in straight sets. In the second set the discomfort was evident as restricted movement forced him to score a blank as sixth seed Jishnu Vardhan wrapped up the proceedings 6-4 6-0.

''I have been carrying this ankle injury into the tournament as the stakes were high. A win here meant a wild card in the Chennai Open. But now it is bad and I don't even know if I can play the qualifuers in Chennai, '' Ashutosh said.

Fazaluddin's tennis holiday also ended s VM Ranjeet showed him the door 6-1 6-2.