Record-breaking Root edges England closer to Sri Lanka victory
Root, who equalled Alastair Cook's record during the first innings of the second Test, made 103 from 111 balls for his 34th Test ton.
England resumed on 25-1 at the start of day three, with Root leading the way for the hosts and the crowd rose as one when a sweeping four completed his landmark century.
He helped his nation set their opponents a target of 483 after they were 251 all out.
As the light faded over Lord's, so too did Sri Lanka's momentum in their record-attempting chase, with Gus Atkinson and Olly Stone claiming Nishan Madushka and Pathum Nissanka respectively.
Play was eventually halted due to bad light, and called off to be resumed on Sunday with the tourists at 53-2 with Dimuth Karunaratne (23) and Prabath Jayasuriya (three) at the crease.
Data Debrief: Root revels on record-breaking day
Day three of the second Test belonged to Root, whose century was also his quickest in Test cricket.
Adding to his 143 in England's first innings, he registered two tons in a match for the first time, while becoming only the fourth player to achieve that feat in a Test at Lord's.
Root also joins Brian Lara and Sachin Tendulkar in scoring 5,000 Test runs in two different decades, while closing the gap on Cook's all-time England tally (12,472) to just 95.
If that was not enough for him, he also took the catches for both of Sri Lanka's wickets, making him the first England player to reach 200 in Test cricket.