Aston Villa maintained their unbeaten start to the season with a goalless draw at Watford - but they missed enough chances to have won the game comfortably.

Although Watford fought back in the second half, Stiliyan Petrov, Gabriel Agbonlahor and Steven Davis all squandered opportunities during the first 45 minutes which, if taken, would have rendered the rest of the match academic.

Villa found Watford goalkeeper Ben Foster in inspired form, but they were thankful in the second period that Thomas Sorensen was equally sharp.

The Denmark international made superb saves from Malky Mackay, Marlon King and substitute Hameur Bouazza to leave Watford still searching for their first Barclays Premiership victory.

Adrian Boothroyd's team were outplayed in the opening period, but they showed plenty of courage and spirit after the interval.

Villa boss Martin O'Neill kept the side who began last weekend's 1-1 draw at West Ham, while Jordan Stewart replaced the injured Chris Powell for Watford.

It was O'Neill's men who took control of the game quickly and they almost went ahead twice in the ninth minute.

Agbonlahor's low ball from the right wing caused confusion in the Watford penalty area, allowing Juan Pablo Angel to find space and hit a 12-yard effort which was blocked by Mackay.

Seconds later Agbonlahor found Petrov, whose run from midfield had gone unchecked, but the Bulgarian's close-range shot was saved by Ben Foster.

In the 12th minute Agbonlahor - who spent a month on loan at Watford last season - was denied by a superbly-timed tackle from Mackay and then Davis sent an angled drive inches wide of the left post after being teed up by Angel.

After 28 minutes Angel, who was linking the play superbly in the centre-forward role, played a clever pass to set up defender Liam Ridgewell, who was allowed to charge unchallenged into Watford territory before delivering a low cross that Stewart and Gavin Mahon just about managed to clear between them.

Ashley Young was Watford's most dangerous attacking player, and from his intelligent pass King struck a 12-yard shot that hit Gareth Barry and went behind.

But Villa wasted another good chance to take the lead 10 minutes before the break.

Agbonlahor left Stewart trailing as he sped into the penalty area onto Olof Mellberg's lofted pass, but the young forward could not beat Foster, who pushed away his eight-yard attempt.

Mackay thwarted Villa again in the 40th minute with an excellent intervention to deny Angel, who was preparing to shoot from 10 yards after controlling Luke Moore's knock-down.

Villa continued to pile on the pressure and only more alert goalkeeping by Foster stopped Petrov from putting his team ahead after a brilliant one-two with Angel.

After the break the pattern of the first half was quickly resumed, with Villa going close on two more occasions.

Foster flew to his left in the 50th minute to palm away Agbonlahor's venomous left-footed drive from 22 yards and seconds later Angel somehow scooped the ball way over the bar from seven yards after Agbonlahor had picked him out.

Angel was again wasteful in the 58th minute when he headed Davis' left-wing cross wide from six yards after outjumping Mackay.

Villa were almost punished twice in the next minute, staying level thanks only to two brilliant saves from Sorensen.

The Danish goalkeeper kept out half-time substitute Bouazza's 20-yard with a fine low stop to his right and then made an even better save to push away King's powerfully-struck angled volley after Mackay had won the ball in the air.

Sorensen made a third stunning save in the 69th minute when he blocked Mackay's point-blank header from Young's corner.

Bouazza, who made a big difference for the home team, combined with Young in the 76th minute to set up King, whose shot wrong-footed Sorensen from 20 yards but slid past the left post.

Four minutes earlier King had been frustrated when Tommy Smith failed to give him the ball after tricking his way past Ridgewell and Barry.

Smith's influence on the right wing had grown as the half progressed, but Boothroyd surprisingly chose to replace the recent signing from Derby with Tamas Priskin in the 78th minute.