Nathan Lyon undid Sachin Tendulkar and a couple of other batsmen with balls that weren't too full, pitched in line and straightened enough © BCCI Enlarge

Halfway through this tour, Nathan Lyon's place as Australia's first-choice spinner appeared to be in serious doubt. He had been dropped after leaking runs heavily in the first Test in Chennai and the coach Mickey Arthur said Lyon "hasn't gone that well this year" and needed to work on some technical issues. It was hardly what Australia wanted halfway through an India tour and with an Ashes battle looming.

Whatever Lyon has been working on, the results showed on the second day in Delhi. Shane Watson did not call on Lyon until the 20th over of India's innings, when M Vijay and Cheteshwar Pujara had already made a flying start of 78 for 0. Immediately, Lyon troubled the batsmen. He deceived Pujara with an arm ball that clipped the off stump after beating the outside edge and by the end of the day he had 5 for 94, an outstanding result given his struggles earlier in the tour.

Two things stood out about Lyon's performance. One was how much of a threat he posed when coming around the wicket, a tactic that he all but ignored at the start of the series. The other was a change in length. Lyon had bowled too full earlier in the tour and that was a key factor in his inability to restrict the runs. Men like MS Dhoni, who blasted a double-century in Chennai, will always feast on full, slow balls wide of off stump.

That's precisely what Dhoni did early in his innings in Delhi when Lyon overpitched a couple of times: the ball was driven handsomely through cover for four. But when he brought his length back and bowled a touch quicker he negated the chances of the batsman coming down the pitch. They had to find other ways to handle him, often by playing back, and when combined with his around-the-wicket line it made Lyon dangerous.

Suddenly, every ball brought the threat of an lbw if Lyon could just pitch it in line and straighten it enough. Three of his wickets came via that method. First there was Virat Kohli, who played back and misjudged the line. Then there was Sachin Tendulkar, who had already survived a perilously close lbw shout when he tried to sweep Lyon. He fell when he played back and couldn't get his bat down in time. And from the last ball of the day, Lyon had his fellow offspinner R Ashwin the same way.

Who knows what might have happened if Lyon had tried a similar approach earlier in the series. His success has come too late for Australia to retain the Border-Gavaskar Trophy but for Lyon's own future this was an important performance. Before this match, Lyon's recent record was disappointing: in his eight Tests since the start of the Australian summer he had taken 25 wickets at 47.52 with a best of 3 for 41.

Xavier Doherty and Glenn Maxwell had both been used in this series without suggesting that they were the long-term answer for Australia. But back home, the left-armers Steve O'Keefe and Ashton Agar were accumulating wickets in the Sheffield Shield, while the legspinner Fawad Ahmed was also pushing his case for consideration whenever his citizenship comes through. Lyon's work in Delhi will remind the selectors why he has been their No.1 choice for more than 18 months.

Of course, Lyon might not have been so successful were it not for the pressure being built at the other end by Australia's fast men. They were quick, accurate and used the odd bouncer to keep India's batsmen wary, and it was comfortably Australia's best team bowling effort of the tour. It wasn't enough to give Watson's men a first-innings lead, but the outcome after two days in Delhi was as even between India and Australia as at any stage throughout the series.

The day's play also confirmed Lyon's place as Australia's best Test spin option - 72 victims so far in 22 Tests attest to his wicket-taking habit. He could yet add more on the third morning and will be a key man in India's fourth-innings chase. And you can bet Watson won't wait 20 overs to introduce him again.