Joe Root and Matt Prior made heartening returns to the scene of previous successes as England's new Test era passed the first examination of its credentials at Lord's.

Root, at the ground where on his last Test visit he made a career-best 180 as an opener against Australia 11 months ago, was back with an unbeaten 102 at number five as England reached 344 for five on day one of the Investec series against Sri Lanka.

Prior, such a marginal choice in many minds to play here after being dropped during England's descent to Ashes whitewash last winter and then hampered by injury this summer, restated his case as first-choice wicketkeeper-batsman with 76 not out - at a venue where he made a century on debut back in 2007.

The best efforts of both, in an unbroken stand of 135, were badly-needed as England recovered from 22 for two thanks first to Ian Bell (56) and then Root's alliances with Test debutant Moeen Ali and Prior.

Root, also dropped last winter, produced a chanceless innings on which England can build a future in this match and well beyond; Prior made the most of one early escape, which encapsulated the fine margins of cricket when he avoided an lbw departure for what would have been a second-ball duck only because 'umpire's call' came to his rescue.

It was the early failures of both openers, captain Alastair Cook and debutant Sam Robson, which put the onus on England to dig themselves out of trouble.

A pitch tinged a suspicious shade of green persuaded Angelo Mathews to bowl first, despite sunny skies, and the new ball mostly swung rather than seamed for Nuwan Pradeep and Nuwan Kulasekara.

Cook, hoping to set the tone as England try to put distance between themselves and their miserable winter, cut the fourth delivery of the Test summer for four off Kulasekara.

Robson was under way second ball with a push to cover off the same bowler.

Sadly, the Australia-born opener was not to add to that single before misjudging Pradeep's swing down the slope from the nursery end and edging behind.

Cook's attempt to cut Kulasekara then resulted in an inside edge on to his stumps.

Gary Ballance and Bell, in respective new positions at three and four, had a significant challenge on their hands.

They fared well until Ballance edged an attempted off-drive from deep in his crease to become Pradeep's second caught-behind victim.

Bell added 46 with Root, reannouncing himself in early afternoon by advancing to hit Rangana Herath for six over long off in the first over of the session.

A seventh boundary, cover-driven off Shaminda Eranga, took him to his 50 from 69 balls.

But the bowler soon had his revenge when he beat Bell's forward push, hit him in front and then overturned Paul Reiffel's initial not-out lbw verdict on review.

Moeen was granted six sighters by Eranga, and played a shot at none, before getting his Test career under way when he clipped the seamer for four off his legs.

England's fifth-wicket pair were largely unhurried, save for Moeen's occasional attacking intent - apparent again when he greeted the return of Herath by hitting him immediately over wide long on for six.

Root relied more on his trademark bustle, missing no opportunites to rotate the strike and was notably ready to get forward and disprove a gathering consensus that he more often than not does not do so.

Their contrasting approaches combined for a partnership of 89 until Moeen tried another big hit at Herath, switched to the pavilion end, and edged to slip.

Prior's close shave came in the same over, Herath snaking the ball past the inside-edge of a forward lunge to hit the back leg - only for DRS to rule impact was not decisively in line with off-stump, and Reiffel was therefore vindicated this time.

Thereafter, Root and Prior's progress was seamless.

There were just two boundaries in Root's first 50 but another six on the way to his third Test century, from 183 balls, as he gradually grew more expansive.

Prior was typically more adventurous, bringing up only a second half-century in his last 20 England innings with a characteristic square-drive for his fifth four in Pradeep's solitary over with the second new ball.

Together, they put their team bang on course to top 400 for the first time since Wellington in March last year - 14 Tests ago.Joe Root and Matt Prior made heartening returns to the scene of previous successes as England's new Test era passed the first examination of its credentials at Lord's.