Before India's epic 2-1 series win, England were the only overseas team to win a series in Australia after losing the first Test. They did it three times, but the last of those instances had been in 1954-55. That an Indian team severely hit by injuries replicated that feat illustrates how monumental an achievement this is. Here is a look at the key numbers from the series, some of which also highlight the odds that this Indian team overcame.
The experience gap
Going into the fourth Test, India's playing XI had 13 Test wickets in all (two of which belonged to Rohit Sharma), compared to 1033 for Australia's bowling attack. That stat encapsulated the gap in experience between the two teams in the series decider.
Over the entire series, the average experience for an India player was 31.6 Tests, while that for an Australia player was 42. The difference of 10.4 is the second-highest in any series of three or more Tests in Australia which was won by the visiting team. The only instance of a more inexperienced team, relative to the Australian team, winning in that country was in the 1911-12 Ashes, when the difference in the average Test cap was 11.5.
Debutants make their mark
The fact that India beat Australia despite losing so many of their first-choice players is largely because their replacements did so well. The five players who debuted in this series contributed 20.4% of India's runs (off the bat) and 36.9% of their bowler wickets. Shubman Gill scored 259 out of the 371 runs scored by India's debutants, while Mohammed Siraj picked up 13 of their 24 wickets. And these numbers exclude the vital contributions of Shardul Thakur, who, playing his second Test, scored 69 and took seven wickets.
In India's Test history, there have only been five instances when players who debuted in an overseas series of three or more Tests collectively contributed 20% of the team's runs and wickets. Two of those were in the 1940s, while the others were in England in 1996 (when six players debuted, including Sourav Ganguly, Rahul Dravid and Venkatesh Prasad), and in the West Indies in 2011, when Virat Kohli, Abhinav Mukund and Praveen Kumar made their debuts.
India's second innings in Adelaide lasted just 21.2 overs, but in the remaining six innings (excluding the Melbourne knock when they needed 70 to win) they faced more than 90 overs every time.
In the last 40 years, there has been only once instance of an overseas team batting 90-plus overs more than six times in a series in Australia - West Indies in 1988-89; that was also the last time Australia lost a Test at the Gabba before the defeat against India. West Indies won the 1988-89 series 3-1.
No fourth-innings blues for India
In each of the last two Tests, Australia went into the fourth innings of the game as favourites. Each time, they were thwarted by the skill, resilience and determination of India's batsmen, who batted 131 overs in Sydney for a draw, and 97 in Brisbane to seal the win. Essentially, the difference between a 3-1 scoreline in favour of Australia and the result which eventually transpired were these fourth-innings performances.
India's fourth-innings average in the series was 52.35, which is the fourth-highest in the last innings by an away team in Australia (with a cut-off of 900 balls faced and at least two fourth-innings efforts). Among the 34 series that make the cut-off, the last time a team did better was in 2008-09, when South Africa averaged 57.93 in the fourth innings, thanks to the record run-chase of 414 for 4 in Perth, which was followed by another successful chase of 183 for 1 in Melbourne.
In the last 40 years, there have only been four instances of an overseas team playing 90-plus overs twice in the fourth innings in an Australian series, which includes the 2008-09 series mentioned above. In fact, all four instances have happened in the last 15 years, suggesting that fourth-innings batting in Australia is perhaps not as difficult as it used to be in the 1980s and 1990s.
For India, this was the third instance of batting 540 balls or more (90 six-ball overs) twice in the fourth innings of an overseas series. The two previous occasions were also in Australia, in 1967-68, and then again 10 years later; both were during the era of eight-ball overs. Unlike in this series, though, all of those batting efforts came in losing causes.
In both their fourth innings, in Sydney and Brisbane, Cheteshwar Pujara did the job of stalling Australia's early quest for wickets, facing 205 deliveries in Sydney and 211 in Brisbane. His total tally of 420 deliveries in the fourth innings has been bettered only three times in an away series in the last 40 years; one of those was by Murali Vijay on the 2014-15 tour to Australia.
When the toss didn't matter
As if the unavailability of so many players wasn't bad enough, India also lost the toss in each of the last three Tests. That didn't stop them from winning two of those matches, though, making it only the fifth time in the last 40 years that a visiting team has won multiple Tests in Australia after losing the toss.
The only occasion during this period when Australia lost three Tests despite winning the toss was in 1988-89 - yes, that series again - when West Indies won in Brisbane, Perth and Melbourne.
For India, this was the fourth instance of winning multiple Tests in an away series despite losing the toss. They had earlier achieved this against West Indies (2019), Bangladesh (2009-10), and New Zealand (1967-68).
In fact, the three results in this series all went in favour of the team which lost the toss, which continues a recent trend: since the start of 2020, teams losing the toss have a 15-8 win-loss record in 27 matches.
Slim pickings for Lyon, Starc
Nathan Lyon's 100th Test didn't go as he would have liked, and neither did the entire series. Needing 10 wickets to reach the 400 mark, he finished with nine at an average of 55.11. Only once has he averaged worse in a home series: 57.66, against South Africa in 2016-17. On that occasion South Africa's spinners averaged 58.1, but here Lyon was comprehensively outbowled by India's spinners, who took 23 wickets at 27. The difference of 28.1 between the two averages is the highest by far in any home series that Lyon has played.
There are only two other instances when Lyon had a worse average than the opposition spinners in a home series: against Sri Lanka in 2012-13, and against India in 2018-19. On both occasions, the difference was fewer than five runs per wicket. (Click here and scroll down the page for a full list of Lyon versus opposition spinners in home series, updated till before his 100th Test.)
As if Lyon's sub-par form wasn't bad enough, Mitchell Starc was also off-colour through much of the series. His opening over to Mayank Agarwal in Melbourne contrasted sharply with his wayward bowling through most of the Gabba Test. Starc finished with a series average of 40.72, which made it two Australian bowlers bowling 100-plus overs at averages of more than 40. The last three such instances for Australia have all been against India. Starc and Lyon are in good company, though, for the two bowlers who met with the same fate in the 2001-02 home series against New Zealand were Glenn McGrath and Shane Warne.
The head-to-head battles that mattered
Two batsmen scored 100-plus runs against a bowler in the series, and both instances were against Lyon, who conceded 496 runs, the most by a bowler in this series. Both Pujara and Rishabh Pant had success against him, and those were the battles which probably swung the series in India's favour.
Pat Cummins, the top wicket-taker and the Player of the Series, was outstanding throughout the series, but the one anomaly was his performance against left-handers: he bowled 171 deliveries to them and conceded 91 runs without taking a wicket; Pant scored 56 off 84 balls against him. Cummins averaged 15.38 against the right-handers, taking 21 wickets in 808 balls.
S Rajesh is stats editor of ESPNcricinfo. @rajeshstats