LONDON (REUTERS) - Chelsea are heading for Abu Dhabi next week to try to become world champions but their attacking displays, including in their laboured 2-1 fourth-round FA Cup win against third-tier Plymouth Argyll on Saturday (Feb 5), have been anything but world-beating.

The European champions had to rely on defenders Cesar Azpilicueta and Marcos Alonso for their goals against Plymouth who took an early lead through Macaulay Gillesphey and failed to convert a penalty in the final minutes of extra time.

The visitors' fans, packed into the Shed End, taunted Chelsea with chants of "Champions of Europe? You're having a laugh" as the Blues struggled to turn possession into clear chances, a problem that has beset them for much of the season.

Record signing Romelu Lukaku was largely kept under control by Plymouth's hard-working defence while Moroccan winger Hakim Ziyech and his home-grown peer Callum Hudson-Odoi were also limited to a few chances.

The 1-1 score at 90 minutes was a familiar one to the Stamford Bridge faithful who have seen the Blues draw five of their last seven home games in the Premier League.

Chelsea brought on other big-money signings Timo Werner and Kai Havertz to try to break the deadlock with little effect and only academy graduate Mason Mount posed a consistent threat before he was substituted deep into extra time.

Chelsea coach Thomas Tuchel, who was absent on Saturday after testing positive for Covid-19, has been critical of his attackers during the Blues' recent poor run of form which has seen them drop out of contention for the Premier League title.

Lukaku was dropped for a game after saying he was unhappy with Tuchel's system.

"It's maybe for him a little bit tough right now to score," Chelsea assistant coach Arno Michels told reporters when asked about Lukaku's struggles in front of goal.

"He's a little bit unlucky. We try to give him opportunities, we will keep on going like this," Michels said.

"He needs also some trust in moments when he does not score."

Chelsea have scored 48 goals in the league this season, 10 fewer than Liverpool who sit one rung above them in second place in the table and who have played two games less than the Blues.

Lukaku has contributed only five goals, one less than midfield lynchpin Jorginho and two fewer than Mount.