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He once again helped rescue England's flaky batting as he hit an unbeaten 107 at a sun-kissed Lord's.
Together with 85 from skipper Alastair Cook, Bairstow's third ton in six Tests dragged the hosts out of a hole in near-perfect conditions for batting.
Rash strokeplay mixed with disciplined bowling from Sri Lanka had reduced Cook's men to 84-4 just after lunch.
But Bairstow profited from a dropped catch and then the most marginal of lbw decisions to continue his wonderful early summer run of form.
Not since beating India 4-0 in the summer of 2011 have England whitewashed a Test opponent in a series of three or more matches.
And while the weather forecast for the remainder of the match is uncertain, Bairstow's fightback has given them a hold in a contest that had been drifting Sri Lanka's way.
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While England have improved both in style and substance over the course of the last year, serious flaws remain - and the vulnerability of the top order is the most pressing of all.
On a true pitch and under benign skies, they once again lost key wickets cheaply - four this time for 28 runs, having chosen to bat and looked completely untroubled in the first hour of play.
First Alex Hales lost patience, having been kept runless for 22 balls, heaving unnecessarily at Rangana Herath to send a looping edge to Angelo Mathews at slip.
Then Nick Compton, mired in a horrible trot of form and seemingly bereft of confidence, chased a wide half-volley and edged Suranga Lakmal behind for just one.
Joe Root followed four runs later, pinned lbw by the same bowler after the initial not-out decision was correctly overturned by the third umpire, and when James Vince had his bail removed by Nuwan Pradeep for 10 just after lunch, England had slumped from 56-0 to 84-4.
Compton's dismissal was the most chastening of all: to a ball that should have been routinely driven away for four, greeted by a ghastly silence from the near capacity crowd, followed by a slow walk back to the old pavilion, Lord's suddenly the loneliest place in London.
It could have been worse had Shaminda Eranga held on to a straightforward chance at mid-wicket when Bairstow was on 11, the ball flying straight into his hands and out again.
But the Yorkshireman, a stark contrast to Compton this summer in terms of sweet touch and confident animation at the crease, continued to play his shots with Cook in more sedate style at the other end.
Cook reached his fifty off 89 balls - his first half-century of the series - and the only surprise was that his unflustered progress ended on 85, Pradeep trapping him lbw with a fine inswinger from round the wicket.
Bairstow then had his second life, given not out to an lbw shout from Eranga on 56 when the review indicated that the ball appeared to be hitting enough off leg stump to send it cartwheeling away.
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Had the original decision been out he would have been walking, but instead he settled in with first Moeen Ali and then Chris Woakes as afternoon turned to evening and the ball lost its shine and shape.
By his aggressive standards it was a patient innings, but when offered anything overpitched or wide by a hard-working and parsimonious attack, he took full advantage.
His first Test century at Lord's came with a tickle off the hip from his 160th ball as the evening shadows stretched across the pitch, and he celebrated in fitting style - helmet off, arms stretched out wide to the grateful crowd.
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England's Jonny Bairstow on Test Match Special: "I am delighted. It was a bit scratchy but sometimes you just have to find a way to get there. The ovation at the end was something special."
Former England batsman Geoffrey Boycott: "Bairstow sees it as scratchy - we see it as nicely batted. And it's a good job he was dropped because England would have been in real trouble. This middle order has got them out of jail."
"England haven't had a great day. This isn't a great return for winning the toss - sunny day, good pitch. Whether it's enough depends on when we see Sri Lanka bat."
Former England captain Michael Vaughan on Nick Compton: "He has struggled all summer. He needed a number on a true wicket against a straightforward attack.
"It is a lonely world - international sport - when things are against you. He doesn't bring energy at number three. He doesn't have those gears."
Jonny Bairstow's second century of the series helped England recover from another top-order collapse to reach 279-6 on day one of the third Test with Sri Lanka.