Jennings jumps the Test queue after arriving early for his bus

Trott: Looked like Jennings has been playing for two years (2:38)

Keaton Jennings becomes the 19th England batsman to score a century on Test debut (2:38)

It's hard to believe that Keaton Jennings' day started in panic.

So calm did he look in compiling a century in his first Test innings - the first England opener to do so since Andrew Strauss in 2004 (Alastair Cook's came in the second innings of his debut in 2006) - that it was hard to imagine him waking at 5am, fearing he had missed the bus to the ground and throwing his kit together in a rush.

For most of the rest of the day he looked supremely assured and unruffled.

Has anyone ever brought up a century on Test debut before with a reverse sweep? It seems unlikely.

But it was a mark of Jennings' confidence that, throughout the second half of his innings, he played the shot when the opportunity arose. He seemed to be waiting for the delivery on off stump and, combined with his no-nonsense treatment of the short ball and his long stride enabling him to put away the full one, he produced the most assured England debut for… almost a month.

For a team that couldn't find an opening partner for Alastair Cook for years, England suddenly have an embarrassment of them. That old cliché about London buses springs to mind.

It is hardly a problem. There seems no reason why one of the top three - presumably Jennings or Haseeb Hameed - could not bat at No. 3 and allow Joe Root to move back to No. 4. With Jonny Bairstow at No. 5 - his position for the foreseeable future - and Ben Stokes at No. 6, an England line-up searching for solidity for some time might be taking shape.

These are early days, of course. Jonathan Trott, in 2009, was the last England player to make a century on Test debut and we now know that, under that apparently calm exterior, the anxiety was building. The relentlessness of modern international cricket is part of the challenge and that is all to come for Jennings. Perhaps the fact that he and Hameed are nowhere near selection for the limited-overs team may turn out to be a blessing.

This innings was a reminder, too, of the absurdly small margins that separate success and failure. Had Jennings edged his ninth delivery - a nervous push away from his body as he sought to get off the mark - or been caught off his tenth - a fence off the back foot that lobbed just over gully - he would have been dismissed for 0 and under pressure immediately. He was always going to play the next Test, in Chennai, but unless he had scored heavily in one of the four innings available to him, it was hard to see how he would win another opportunity in the near future. This was potentially a life-changing opportunity and he seized it.

Until a few months ago, Jennings looked a solid but limited player. He was, in essence, an accumulator. And there's nothing wrong with that, even if in modern cricket - and especially in this England side - it is an unfashionable quality.

He owes his greater range of stroke, and his confidence to play them, in part to the opportunities he has won in Durham's T20 side. An unlikely team member until recently - even at the start of the 2016 season, he was in their side as a bowler and came in to bat at No. 9; his first 13 T20 games brought him a combined total of two runs - he was given the freedom and encouragement to expand his range. After all, there's no point playing like a traditional opener if there are only a few deliveries left in the innings.

While the results were not immediately obvious - the 88 he scored in the T20 Blast final was his first half-century in the format - it pushed him out of his comfort zone, taught him new tricks and showed him that he could pull them off.

The benefits were especially obvious in the second session. With India bowling a tighter line and length, Jennings' run-scoring opportunities might have dried up. Indeed, having reached 64 from 107 deliveries, it took him another 34 to reach 70. The constrictors seemed to be tightening around his neck.

But then, seeing the gap in the field and the line of the ball from Jayant Yadav, he unleashed his first reverse sweep - and he does sweep rather than just make contact - to send the ball speeding to the third-man boundary. The effects were immediate with Yadav, perhaps just a little disconcerted, over-pitching next ball and Jennings taking the opportunity to drive through the covers for four more. The shackles were, if not released, at least relaxed. Virat Kohli and his bowlers suddenly had to think harder about their fields and their lines of attack. Three times in that middle session, Jennings picked up boundaries with the reverse sweep; that's 12 of the 38 runs he mustered in the 31 overs.

It was noticeable he took fewer liberties against Ravi Ashwin. Ashwin's mastery of flight and variations are causing England huge problems in this series but, although Jennings did not hit him for a single boundary, he was able to eke out 23 from 66 balls against him. Once or twice he skipped down the pitch and then cut the resulting shorter ball and several times he swept, but generally he played him with a patience and composure that bodes well for the future.

"The reverse sweep has been a shot over the last six to eight months that, touch wood, I've played fairly successfully," Jennings said later. "I suppose at that moment [on 96] I looked at the scoreboard and thought 'Well, would I rather get out caught first slip defending or at first slip trying to get to a hundred?'

"So I bit the bullet and went for it. Thankfully it hit the middle of the bat and went for four."

The foundations of Jennings' game had been built long before his T20 experiences with Durham, though. Back in those net sessions with his dad, Ray. Back when he was learning the compact technique that helped him leave well, after those couple of early indiscretions, yet still put away the short or over-pitched ball without fuss or extravagance. Back when he was developing that stance, far back in the crease, but still ensuring he was quick to come forward. He made it look simple and he made it look as if little could go wrong with his technique. And, most of all, he made it look as if he had been with this squad for months, not a few days. Those are all encouraging signs.

Without those foundations, the decorative elements - the sweeps, in particular - wouldn't have meant a thing. But the combination… this is a man who can fit in very well with this England set-up.

Where does all this leave the game? The England management feel that a score of 350 - somewhere around 30 better than the first-innings average here compared with the most recent five Tests - might prove highly competitive. They also feel that this may be the pitch that results in the shortest match of the series.

The India camp takes a different few. They argue that there was just a little damp in the surface and that is what caused the turn. As a result, they suggested batting on the second and third days may be easier and it is true that, in those last five Tests, the second-innings scores have tended to be around 50 runs higher than the first innings. The third and fourth innings scores drop sharply, however, so a first-innings lead is likely to prove defining.

That renders the last hour or so of the first day - when Jos Buttler and Ben Stokes weathered some agonisingly close moments - all the more crucial. The game could well have drifted away from England in that time but both men had the presence of mind to know that, for all the talk about positivity - talk they embrace and embody as much as any of their team-mates - this was a time to graft and fight, not attack and plunder. That they did it so well suggests they are learning the balance between attack and defence required and keeps England in with a chance in this match.