LONDON (AP) — A Joe Root century and half centuries from Matt Prior and Ian Bell spurred England's comeback against Sri Lanka and ultimately the advantage at 344-5 after the opening day of the first test at Lords.

Root and Prior ended a sunny Thursday unbeaten on 102 and 76 respectively. Bell contributed 56 and Moeen Ali 48 on debut in a middle-order fightback by England, which was 74-3 in the first session.

Root said England must make its advantage count on day two.

"There was a period in the middle where scoring wasn't quite as fluent," Root said after his third test century in his 16th match. "The challenge of trying to score runs after the winter we had is something I relish. We've built a good platform now. We want to make 400 plus, and make it hard work for the Sri Lankans."

Sri Lanka won the toss and chose to bowl, encouraged by green areas on the pitch.

The decision paid off quickly, as pacer Nuwan Pradeep dismissed Australian-born debutant Sam Robson for 1 in the fourth over, and Nuwan Kulasekara bagged captain Alastair Cook, chopping onto his stumps on 17 in the sixth.

Things got worse for the hosts when Pradeep dismissed Gary Ballance with a catch behind for 23, leaving England wobbling on 74-3.

But Bell began to offer some resistance in his 99th test, making a 56 that included a six off Rangana Herath in the first over after lunch. He fell lbw to Shaminda Eranga, which brought in Ali.

He played confidently in his test debut, striking six fours and one six on the way to 48, but ran out of patience trying to reach 50, not long after Root. A big swing gave only a nick to first slip. But Ali and Root had England back in charge with a stand of 89 at 209-5.

By this point, any color in the wicket had faded under the sun, and Sri Lanka struggled to put any further pressure on the assured figures of Root and Matt Prior, who batted and ran aggressively.

Root brought up his century, off 183 balls, with a three from a shot through midwicket off Herath.

Prior, tipped by many to be replaced in the test side by Jos Buttler, escaped a huge lbw shout on only his second ball, and didn't look back. He thrashed nine fours on his way to 76.

By stumps, their partnership was worth 135 for the sixth wicket.

Sri Lanka bowling coach Chaminda Vaas believed his players can start the second day as well as they did the first.

"There was something on the wicket, the bowlers gave 100 percent and took five wickets but after lunch, it got flat," Vaas said. "It's not easy, test cricket is patient, and we need to bowl in good areas."