Root added another 98 runs on day two of the first Investec Test to finish 200 not out as England posted 575-9 declared, improving on their 551-6 against these opponents here eight years ago.
But after Sri Lanka replied with 140-1 at stumps, Kaushal Silva making an unbeaten 62 on a pitch offering little encouragement to any bowlers yet, England appeared to be engaged in a long haul to consolidate their advantage.
Root’s 298-ball innings lasted almost eight-and-a-half hours, contained 16 fours and came on the same ground as his previous-best 180 against Australia last year.
He first took guard at 74-3, with England still seeking a foothold at the start of their new Test era after last winter’s Ashes whitewash, and went on to share four stands in excess of 50.
The highest was for the sixth wicket with Matt Prior (86), which ended on 171 after a change of tactics from the Sri Lankans on another sunny morning.
Root was subseqently joined by free-scoring trio Chris Jordan, Stuart Broad and Liam Plunkett, then finally James Anderson in an unbroken last-wicket partnership which closed only when the 23-year-old Yorkshireman paddle-swept Rangana Herath for the two runs he still needed for his 200.
Shaminda Eranga had bounced out Prior and Jordan as England nonetheless passed the Test benchmark of 400 – something which had proved beyond them since March 2013, in Wellington. Prior had a largely uncomfortable experience, after Sri Lanka went short at both him and Root with an uncompromising leg-side field in place.
The aggressive approach, in keeping with captain Angelo Mathews’s pre-match promise, paid off after 45 minutes in which Prior could add only 10 runs.
He did go past 4,000 in Tests in the process, before Eranga –round the wicket, with six leg-side catchers – produced a delivery he could only fend into the hands of short-leg.
Prior’s departure brought England’s third debutant to the crease, and Jordan soon looked at home – off the mark against Eranga with an all-run four through vacant mid off and then up the wicket to time Herath wide of mid on for a boundary.
He hooked Eranga tantalisingly over the head of long leg and the next ball brought up that elusive 400 in style with a back-foot punch past point for another four.
Eranga got his revenge in the same over, Jordan bailing out of another pull only to somehow loop a simple catch behind to Prasanna Jayawardene.
But Broad quickly joined in with a spree of five boundaries in nine balls – three in Nuwan Kulasekara’s first over of the day.
His carefree attack brought him 41 runs in the 50 stand and allowed Root to tick over at his own pace – until Broad holed out pulling Nuwan Pradeep (4-123) just before lunch.
Plunkett had an early escape, dropped at midwicket on only two off Pradeep, and Anderson also had a couple of scrapes – a tight lbw call and a missed chance at slip. But the tail did enough to help Root to his notable landmark.
If England did not already realise wickets would be hard-earned, seven overs with the new ball before tea gave them further insight.
Dimuth Karunaratne had two close calls.
He was given out initially lbw to Anderson on five, only for DRS to show the ball clearing leg stump. He then edged Broad at catchable height between second and third slip.
The opening stand with Silva reached 54 before first-change Jordan struck with only his third ball in Test cricket.
A full length outside off stump was the simple formula for Karunaratne’s edged drive behind, a regulation dismissal which hinted falsely that others might follow. They did not.
Kumar Sangakkara, in perhaps the final Lord’s appearance of his outstanding career, took advantage when Jordan welcomed him by twice over-pitching on to his pads.
Thereafter, the former Sri Lanka captain was in no-risk mode – and the nearest England came to disturbing his and Silva’s second-wicket partnership was when Broad momentarily thought he had the opener caught-behind on 39 only for the third umpire to rule the outside edge had not carried.
Instead, Silva had a half-century to his name by the close –reaching the milestone when he edged Anderson just short and then past second slip for his ninth four.