IT took the advent of Specsavers as the competition's sponsors for Keaton Jennings to gain sight of his fourth County Championship century.

It was a long time coming after his 103 at home to Sussex in the middle of the 2014 season, but it was worth the wait as he skilfully held the Durham innings together against Somerset at Emirates Riverside.

With 50 minutes to bat under what had been clear skies for most of the day, Somerset struggled to 30 for three.

Chris Rushworth gained lbw verdicts against Tom Abell and nightwatchman Josh Davey, then 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 and Jennings said: “It has put us on the front foot.

“Our total could be above par, depending on how we bowl tomorrow. From a personal point of view to start the season with a good score is awesome.

“I got a bit lucky with playing and missing and it's a pitch where you never really feel in or that you can move the board along. You have to stick in and Jack Burnham and Usman Arshad did that really well.

“I played a bit in South Africa in January and February, so it was about 25 degrees colder here. Riverside is a nice place to play but there are not many pitches around the world like these and I have learnt a lot playing on them.

“I have learnt how to handle hardship and failure, but to be back opening the innings is an honour and I am thankful for the opportunity.”

The first day of the season proper brought the sort of blue skies which would normally persuade captains to bat. But the new rule allowing the visitors to bowl without bothering to toss was invoked with mixed results for Somerset's new skipper, Chris Rogers.

When his opposite number, Paul Collingwood, was bowled first ball Durham had slipped from 134 for two to 159 for five.

Ryan Pringle then drove to extra cover, but Jennings found a staunch ally in Arshad in a stand of 72.

In looking to press on before the new ball was taken, Jennings fell for 116 when he top-edged an attempted pull and was caught at gully.

With their cornerstone gone, Durham folded with the last four wickets going down for 12 runs in four overs.

Learning your trade as an opening batsman at Chester-le-Street is a tough apprenticeship and in the last two seasons Jennings has been dropped for the last few games.

But at 23, the South African looked the finished article as he patiently built his 201-ball century then expanded his repertoire to include a perfectly-executed reverse sweep.

That came off the left-arm spin of Roelof van der Merwe, a South African all-rounder who has played for Holland and whose inclusion raises questions about county cricket's inability to bring on home-grown spinners.

Van der Merwe looked nothing like as good as George Dockrell two or three years ago, but the Irish left-arm spinner was released by Somerset last season.

Jennings lost his place for the last six games last season after an innings of 98 at Lord's in the third match was followed by a top score of 61.

His third-wicket stand of 79 yesterday with Burnham was invaluable, with the England Under 19 batsman looking comfortable and showing excellent judgement of what to leave in taking the score to 134 for two.

He had made 33 when a superb ball from Scotsman Josh Davey beat his forward push to take out off and middle.

Then Gregory took two in two with balls nipping back into the right-handers. The first moved so sharply it looked as though it might have missed leg stump, but umpire Nigel Cowley had no doubt.

The next delivery splattered Collingwood's stumps but the hat-trick ball was short and allowed Pringle an easy two runs through the covers.

But he looked too anxious to move the scoreboard along, leaving Arshad to show a more restrained approach in taking 13 balls to get off the mark.

He scored eight off the first 59 balls he faced, then drove Allenby wide of mid-off for four and Jennings clipped the same bowler to deep mid-wicket for the two runs which took him to his century, which included 13 fours.

Once Jennings departed the rest swiftly followed, championship debutant Brydon Carse 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, but if Rushworth and Onions take up where they left off Durham will be in a strong position.