The first session of the Ashes ended with honours even as England reached 98 for two by lunch at Trent Bridge.

Captain Alastair Cook, who chose to bat first under cloudy skies, was first to go for 13 before Joe Root and Jonathan Trott stabilised things with a stand of 51.

But Peter Siddle hit back for Australia when he parted Root's stumps with a perfectly executed yorker.

Australia would have gone in buoyant had Brad Haddin held on to a tough chance offered by Kevin Pietersen on one, but as it was play will resume with both sides in the game.

Trott, on 37 not out, looked in good touch for the hosts — who scored 72 of their morning runs in boundaries on a lightning outfield.

The tourists sprung a surprise early on, handing a debut to 19-year-old spinner Ashton Agar in place of Nathan Lyon.

The slow left-armer has played just 10 first-class matches but was thrust into the Ashes spotlight in a shock selection.

England's decision to favour Steven Finn over Tim Bresnan and Graham Onions was rather more predictable.

Much has been made of the importance of the first ball of the series, not least since Steve Harmison’s comical effort in the 2006/07 edition.

James Pattinson did not quite reprise that this morning, though he did send down a loopy wide to betray his early nerves.

A bye down the leg side followed, much to the crowd’s pleasure, but Pattinson completed his over without further error.

Mitchell Starc confirmed early suspicions that there was a decent amount of swing on offer, but drifted onto Cook's pads and was flicked for the first boundary of the day.

Australia’s opening pair served up an initial combination of testing deliveries and entirely innocuous ones, with little in between.

Root got off the mark when he turned Pattinson round the corner for four and then guided a thick edge for four more to third man.

It was a surprise when Cook departed at the end of the ninth over, driving hard at Pattinson but nicking through to wicketkeeper Haddin.

Trott was the new man and England proceeded to score almost exclusively in boundaries.

Trott’s first three scoring shots went to the ropes, the first two from consecutive Siddle deliveries, and a dashed single brought the England 50 in exactly 15 overs.

That was the signal for Agar to have his first bowl in international cricket and he promptly produced a full toss that Trott threaded through extra cover for four.

Otherwise, he turned in a promising first spell.

Siddle’s first four overs cost 27, but a change of ends brought immediate results as he produced a superb swinging yorker with his first ball from the Radcliffe Road End to topple Root’s off stump.

Things almost got even worse when Pietersen, playing his first home Test in 11 months, got his bat to a Pattinson ball that was drifting down leg side.

Haddin dived to his left but could not gather the catch as the ball died on him and raced to the boundary.