Indian opener Lokesh Rahul on Sunday said he was disappointed at not being able to capitalise upon the good starts into big score.Rahul batted steadily to score 60 runs with nine hits to the fence and a six before being dismissed while trying to hit a short pitched delivery from Pat Cummins over the onside."Quite honestly, I am not regretting anything. I am little disappointed that I have not been able to convert the starts and get big runs for the team. As an opener, my responsibility is to spend as much time in the middle to get big scores in the first innings so that we don't have to bat in the second innings," Rahul told reporters here."It hasn't been the worst series for me. I got starts, batted really well. Aussie bowlers haven't made it easy. They have challenged us in all the games. Thoroughly enjoyed batting and hopefully one good knock in the second innings might be the time. Might be the knock, I have been waiting for the whole series," he added.Off-spinner Nathan Lyon captured four wickets in the final session to hand Australia an advantage on the second day of the fourth and final cricket Test.Lyon returned figures of 4/67 as India reached 248/6 in their first innings at stumps. Ravindra Jadeja was batting on 16 with Wriddhiman Saha on 10 at the other end when the umpires decided to call it a day.The hosts now trail Australia's first innings total of 300 by 52 runs.Commenting on the behaviour of the wicket, Rahul said the cracks on the pitch play a major role in the coming days."I think the ball will do things off the crack. Even when we bowled on the first day, a few balls did do something funny off the cracks," he added.