FA Cup holders Chelsea were made to fight hard by Gillingham - as is the custom of this competition - before booking a fifth-round meeting with Arsenal.

The Blues claimed their first away victory under Claudio Ranieri, and a first win on the road since April.

But Andy Hessenthaler's battlers threatened to erode the Premiership side's commanding 3-0 lead at Priestfield.

Jesper Gronkjaer, on his full debut following a £7.8million switch from Ajax, was Chelsea's star man.

The Dane netted a first-half double and twice struck the woodwork during an eye-catching display.

In truth, the visitors were aided and abetted in their opening 25-minute goal rush by an over generous home defence.

Eidur Gudjohnsen, who sealed the game in injury-time, was gifted a third-minute opener when Barry Ashby incomprehensibly nodded over his own keeper Vince Bartram, for the Icelandic striker to bundle the ball over the line.

Two pieces of clinical finishing from Gronkjaer, who was allowed the freedom of Priestfield to fire in the first after cutting in from the left and slotted in off Bartram's body in the 25th minute, helped place one foot in round five.

But the battling Gills produced a thrilling comeback with an all-action display after the break.

Paul Shaw side-footed home in the 51st minute and substitute Iffy Onuora caused further panic in the visiting ranks with a header midway through the second period.

As good as Chelsea had been in the first period, they showed glimpses of their worst in the second as the heavy pitch and some hefty challenges took their toll.

Frank Leboeuf, whose proposed move to Monaco appears to have broken down, was stretchered off after halting Shaw's burst that provided the free-kick for Onuora's goal.

Jody Morris followed the Frenchman down the tunnel on a stretcher 12 minutes from the end after taking a knock to his ankle.

But Chelsea's walking wounded, their pride battered by a Gillingham onslaught in the second 45 minutes, shrugged off their problems to seal victory in injury-time.

Substitute Graeme Le Saux found space down the left and crossed for Gudjohnsen to rifle a first-time volley past Bartram from 10 yards.

The Icelandic striker had sealed the game and had opened the scoring within three minutes when Ashby got in a mix-up with Bartram and headed the ball beyond his keeper for Gudjohnsen to force it over the line.

Chelsea fielded four Englishmen in their starting line-up, but it was the foreign connection that had most effect.

Gronkjaer, 23, doubled the advantage on 14 minutes when he cut in from the left and fired a shot across Bartram and in off the far post.

His second, nine minutes later, was crafted by captain Dennis Wise and Gianfranco Zola, who combined to send the pacy winger clear, and after evading Chris Hope's challenge in the area, he slipped the ball into the net via Bartram's body.

Gillingham had gone close themselves in the first period with Carlo Cudicini forced to tip over Nicky Southall's 25-yard free-kick at full stretch and Marlon King driving just wide.

Despite their best efforts, however, a repeat of their 5-0 trouncing in the quarter-final at Stamford Bridge last season appeared on the cards.

Having spent a week preparing for the clash in the hotter climes of La Manga, the Gills, 15th in Division One, seemed to have frozen on the big occasion.

But that was far from the case as Onuora's physical presence, following his half-time introduction, threatened a stirring revival.

First, the striker was halted on the edge of the area by a well-timed Albert Ferrer challenge, the ball teeing up Shaw to sidefoot a response.

Then, with Leboeuf on the stretcher, Onuora looped a header after Cudicini had parried Southall's deflected free kick into the roof of the net.

The majority of the 10,000-plus crowd urged their side forward in search of an equaliser, only for Chelsea, eighth in the Premiership, to highlight their superiority with the finest goal of the match.

Le Saux picked out Gudjohnsen at the back post in injury-time for the striker to fire in and dump the battling Gills.

Teams:

Gillingham: Bartram, Edge, Southall, Ashby, Pennock (Patterson 67), Hope, Smith, Saunders, Lewis (Onuora 45), King, Shaw (Thomson 89).

Subs Not Used: Gooden, Browning.

Booked: Ashby, Patterson.

Goals: Shaw 51, Onuora 67.

Chelsea: Cudicini, Leboeuf (Le Saux 66), Melchiot, Ferrer, Terry, Morris (Stanic 77), Gronkjaer, Harley, Wise, Zola (Poyet 45), Gudjohnsen.

Subs Not Used: de Goey, Hasselbaink.

Booked: Morris.

Goals: Gudjohnsen 3, Gronkjaer 14, 24, Gudjohnsen 90.

Att: 10,419

Ref: D Gallagher (Banbury).