Australia batsman Michael Clarke [Images] expressed disappointment on Friday at missing a century on debut at Lord's while defending his decision to keep playing shots against defensive fields.

Clarke, who has scored a century in his debut Test, dragged a Matthew Hoggard [Images] delivery on to his stumps after scoring 91 on the second day of the first Ashes Test.

He profited from a dropped catch by Kevin Pietersen [Images] on 21 to help Damien Martyn add 155 for the fourth wicket and put the world champions firmly in control after just two days.

"I suppose I'm a little bit disappointed at the way I got out," Clarke told a news conference. "Frustration set in, I played a shot I would like to take back."

Clarke said four overs before he was out he had started to hit boundaries. England [Images] captain Michael Vaughan [Images] responded by getting Hoggard to bowl to an off side field packed with seven fielders.

Vaughan's tactics eventually paid off as Clarke tried to slash a full delivery through the field and managed only to pull it back on to this stumps.

Clarke paid tribute to Martyn, who scored 65. "Damien batted brilliantly, he really toughed it out."

He also said the pitch was much as the same as Thursday, when 17 wickets fell in a frenetic day.

"I don't think there's much difference, especially at the top end. It's still very variable," he said. "The ball was staying low and I think we were pretty lucky England didn't put the ball in the Glenn McGrath area." The Australia pace bowler took five for 21 on Thursday in a 13-over spell.

Pietersen, who top-scored with 57 in England's first innings including 14 from three consecutive McGrath deliveries, said he thought the pitch had improved and expressed confidence that the home team could still win. With three wickets still in hand, Australia lead by 314.

"The pitch got a lot, lot better," he said. "We thought it would get worse. The crucial period tomorrow is how we play McGrath's first spell."

Pietersen, who batted for just under two hours on Thursday for 28, said he had planned to attack on Friday.

"I was always going to be positive this morning," he said. "I really, really enjoyed batting."