NEW DELHI (AFP) - Part-time off-spinner Virender Sehwag picked three key wickets to thwart Australia's grim fightback on the third day of the third Test here on Friday. Sehwag, 30, denied centuries to captain Ricky Ponting (87) and Matthew Hayden (83) before dismissing Michael Hussey (53) as the tourists finished the day on 338 for four in reply to India's imposing 613 for seven declared. They are still 275 runs behind with six wickets in hand and face the unenviable task of batting on a wearing fifth-day track at the Feroz Shah Kotla stadium. The tourists, who trail the four-Test series 1-0 after a 320-run thrashing in Mohali, must avoid defeat here if they are to retain the Border-Gavaskar trophy, with one Test to go after this. Michael Clarke was batting on 21 with Shane Watson on four at close after surviving some close chances against the spinners, who managed to extract good turn from the track.Ponting hit 14 fours in his fine 163-ball knock and also shared a vital 82-run stand with the in-form Hussey. The Australian skipper looked set for his 37th ton following his 123 in the drawn Bangalore opener but was bowled by Sehwag, who gave away just 66 runs off his impressive 22 overs. Ponting is currently second behind India's Sachin Tendulkar (39) in the highest Test century-makers' list."The wicket was turning," Sehwag said after the day's play."I was just trying to contain the batsmen and got wickets in the process. They could not read which way my ball would go. They expected it to spin every time but the ball was actually keeping straight." Hayden, 37, too looked in ominous form, belting 13 fours and a towering six in his 154-ball knock for his highest score in the series so far. The left-handed Queenslander shared 123 runs for the opening wicket with Simon Katich (64) and another 79 with Ponting to lay the platform for Australia's reply. His fine innings ended when he was trapped leg-before with a ball that dipped in sharply. "I had set myself up to bat for a long time but Sehwag bowled really well," Hayden said. "He utilised the conditions as well as any regular spinner would have. The first session will be crucial tomorrow because the longer we bat the more it is going to hurt India." The hosts meanwhile had an injury scare involving leg-spin veteran and captain Anil Kumble. Kumble had to be taken to hospital after he hurt the little finger of his left hand while attempting to take a sharp catch of Hayden at short mid-on. Australia, 50-0 overnight, were off to a steady start with Hayden and Katich putting on their highest opening stand of the series. Katich looked fluent in his strokeplay, hitting 10 fours and completing his 10th Test fifty in the process. Three times he hit paceman Ishant Sharma for fours and also appeared at ease against Kumble, who conceded 53 runs off his 17 overs. Katich was undone by Kumble's leg-spin partner Amit Mishra (1-95) who lured him into playing a flick from outside the off-stump and then watched as the ball sneaked through the gap and knocked off the middle stump. Hayden looked determined to end a poor run of scores, having hit 0, 13, 0 and 29 in the two Tests, and played each ball on its merit. He pulled Mishra over mid-wicket for a huge six to bring up Australia's 100 in the 29th over. The fourth and final Test will be played in Nagpur from November 6-10. SCOREBOARD INDIA, 1st innings: 613-7 decl. (G. Gambhir 206, V. Laxman 200 no; M. Johnson 3-142, S. Watson 2-66) AUSTRALIA, 1st innings: (overnight 50-0): M. Hayden lbw b Sehwag     83 S. Katich b Mishra     64 R. Ponting b Sehwag     87 M. Hussey b Sehwag     53 M. Clarke not out     21 S. Watson not out     4 EXTRAS: (b16, lb3, nb6, w1)     26 TOTAL: (for four wickets)     338 Fall of wickets: 1-123 (Katich), 2-202 (Hayden), 3-284 (Ponting), 4-326 (Hussey) BOWLING: Zaheer     16-4-57-0 (nb1) Sharma     19-5-46-0 (nb2, w1) Kumble     17-3-53-0 (nb1) Mishra     30-7-95-1 (nb2) Sehwag     22-4-66-3 Tendulkar     1-0-2-0. Overs:     105 Toss: India Umpires: Billy Bowden (NZL) and Aleem Dar (PAK) Third umpire: Suresh Shastri (IND) Match referee: Chris Broad (ENG)