KEATON Jennings' sixth first-class century provided the cornerstone of Durham's 256 all out after they were put in by Somerset in their Specsavers County Championship opener at Emirates Riverside.

It took the 23-year-old South African 201 balls to complete his hundred, but its value was underlined when the innings folded rapidly after he was seventh out for 116 as Durham lost their final four wickets for 12 runs.

With 40 minutes to bat, Somerset struggled to 30 for three. Chris Rushworth gained lbw verdicts against Tom Abell and nightwatchman Josh Davey, then in the final over a superb swinging yorker from Graham Onions took out Marcus Trescothick's off stump.

This was bowling of a higher quality than that managed by a Somerset attack relying heavily on Lewis Gregory in the absence of the Overton twins, with Craig suspended and Jamie injured.

Gregory finished with four for 58 when he took the last wicket courtesy of an edge parried by Peter Trego at gully for the diving Jim Allenby at third slip.

Jennings, strong off the back foot through the off side, made a sprightly start with Mark Stoneman when Somerset's new captain Chris Rogers decided there was no need for the toss of the coin.

The openers looked untroubled in reaching 30 in the seventh over, but the decision to switch Gregory brought a double strike.

Tim Groenewald replaced him and found the shoulder of Stoneman's bat for a catch at point with the left-hander aiming for midwicket.

In his first over after the switch Gregory skidded one through to have Scott Borthwick lbw, prompting Jennings and England Under-19 batsman Jack Burnham to rebuild with great patience.

Burnham, showing excellent judgement of what to leave, contributed 33 to a stand of 79 before groping forward to a superb ball from Scotsman Davey which removed off and middle stumps.

That prompted a slide from 134 for two to 172 for six, highlighted by two in two for Gregory with balls which nipped back. The second splattered Paul Collingwood's stumps with the home skipper stuck on the crease.

Ryan Pringle drove Groenewald to extra cover, then Usman Arshad proved even more watchful than Jennings in scoring eight off the first 59 balls he faced.

He then drove Allenby wide of mid-off for four and Jennings clipped the same bowler to deep midwicket for the two runs which took him to his century, which included 13 fours.

Jennings reverse-swept the left-arm spin of Roelof Van Der Merwe for four as he looked to press on before the new ball was taken. But that brought his downfall when an attempted pull off Davey resulted in a skied catch to gully.

The rest swiftly followed, championship debutant Brydon Carse, another South African, falling lbw second ball to Van Der Merwe.

Arshad's useful knock of 32 ended when he missed a swinger from Groenewald in the first over with the new ball.