Striker Eduardo put a year of injury hell behind him to score twice on his Arsenal comeback as they outclassed Cardiff to win their FA Cup fourth-round replay at a canter.

The Croatia international started and finished a fine move for the opener before slotting home a second-half penalty to score his first goals since February 2 last year.

Nicklas Bendtner and Robin van Persie scored the others, with only some fine saves by on-loan Manchester United goalkeeper Tom Heaton keeping the scoreline short of embarrassing for the Welsh.

Five minutes in, Bendtner missed a wonderful chance after neat interplay down the right between Samir Nasri and Bacary Sagna.

Sagna's cross beat every Cardiff defender to find the Dane at the far post only for him to head across goal and wide.

Bendtner had a second fine opportunity a minute later after Carlos Vela's drilled shot was fisted away by Heaton.

Bendtner was first to the rebound but could not steer his shot home.

Arsenal continued to press and William Gallas, still up after a corner, forced Heaton into a smart, near-post save as the Gunners began to lay siege to City's goal.

In the 13th minute Eduardo glanced wide from a Bendtner cross then attempted to break the deadlock in the most spectacular fashion, trying to lob Heaton from 45 yards.

His hopeful strike drifted wide but not before forcing the keeper into a hasty retreat.

Vela then sent the Croatian free with a first-time pass into the area although Darren Purse mopped up the danger.

Purse again kept his side in it, sliding full-length to smother Bendtner's shot from six yards.

By now an Arsenal goal seemed only a matter of time, with skipper Kolo Toure joining his team-mates in attack, jinking inside two defenders and drawing a sprawling save from Heaton.

And with 20 minutes gone, Eduardo had his goal.

Eduardo drove forward towards the Cardiff box, laying the ball off to Vela before continuing his run to head a hanging cross into the net.

He almost had a second moments later but Bendtner's powerful centre would not fall for the striker, who allowed Roger Johnson to clear.

The overworked Heaton nearly gifted the hosts a second when he spilled Nasri's swerving 26th-minute shot but the ball mercifully trickled wide of the post.

Cardiff battled to fight back but had neither the quality nor the possession to put their opponents under pressure.

Instead they slipped further behind, Bendtner beating two markers to head home a 34th-minute corner.

Chris Burke engineered a Cardiff breakaway three minutes before the break with a tidy run down the right, but Arsenal defended comfortably.

Heaton then pulled off two stunning saves, kicking Vela's close-range shot away with an outstretched leg before blocking a point-blank effort from Bendtner who had already hit the post from three yards.

Cardiff looked to be positive as the second period got under way, Jay Bothroyd even pulling off a neat back heel.

Vela continued to catch the eye at the other end of the pitch, though, leaving Johnson dizzy with a weaving run into the Cardiff six-yard box.

To his credit, Johnson recovered to block a shot which would have caused problems at the near post.

Kieran Gibbs, starting at left-back in place of Gael Clichy, surged forward in the 55th minute and his outswinging cross needed a firm clearance by Purse.

Bothroyd finally gave Lukasz Fabianski something to do between the Arsenal posts, drawing a low save with a decent 20-yard effort.

Vela had a penalty shout turned down by referee Mark Halsey after 57 minutes but Eduardo's appeal was upheld three minutes later following a Gavin Rae foul.

Eduardo stepped up himself and slotted home calmly for his second.

Ross McCormack, in an unenviable position fronting the Cardiff attack, hit the wall when a chance, from an inviting free-kick, finally came his way.

Indeed, Fabianski was largely untroubled by Cardiff's players but did appear to be the target of a missile from their supporters.

Eduardo had one opportunity to secure his fairytale hat-trick denied by the impressive Heaton before making way for Van Persie.

Van Persie proceeded to force Heaton into yet another smart save with 11 minutes left, while another replacement, Amaury Bischoff, also went close.

Van Persie, who also hit the post in injury-time, rolled home from Bendtner's assist to make it four in the 89th minute after Cardiff gifted the Gunners possession in the final third.

Teams:

Arsenal Fabianski, Sagna, Toure, Gallas, Gibbs, Nasri (Ramsey 67), Denilson, Song Billong, Vela (Bischoff 74), Eduardo (Van Persie 67), Bendtner.

Subs Not Used: Almunia, Wilshere, Clichy.

Booked: Gallas, Bendtner.

Goals: Eduardo 20, Bendtner 34, Eduardo 60 pen, Van Persie 89.

Cardiff Heaton, McNaughton, Purse (Blake 68), Roger Johnson, Kennedy, Burke, Rae (Scimeca 74), Ledley, Parry (Whittingham 68), Bothroyd, McCormack.

Subs Not Used: Sak, Capaldi, Eddie Johnson, Comminges.

Att: 57,237

Ref: Mark Halsey (Lancashire).