Harlequins fought back from a 14-0 half-time deficit to win their fourth-round Challenge Cup tie against Super League's bottom club Castleford.

Tries from Michael Shenton and Adam Fletcher, plus three goals, put the visitors well clear at the break.

Quins levelled after 53 minutes through Michael Worrincy and Chad Randall tries and three Rob Purdham goals.

And converted tries from Tony Clubb, Danny Orr, David Howell, Gareth Haggerty and Danny Ward saw Quins home.

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Highlights: Harlequins 44-14 Castleford

Harlequins enjoyed the territorial upper hand in the opening 20 minutes but could not make the breakthrough and it was the visitors who struck first in a game played in greasy conditions at the Twickenham Stoop.

Shenton swooped onto a neat grubber kick, muscling past Rikki Sheriffe in the process, and dived over for a good try, with Craig Huby adding the conversion.

Quins came close to hitting back almost immediately through Sheriffe but he lost control of the ball in a tackle as he tried to twist his way over.

Henry Paul conceded a penalty for interference in the tackle and Huby edged the visitors two points further ahead.

Two minutes later Cas engineered a three on two out wide and Kirk Dixon's quick take and pass sent Fletcher over untouched in the corner.

Dixon, who had replaced Huby as kicker after he was injured in a tackle, missed with the conversion, but he added a penalty goal a minute before the break to give the visitors a 14-0 half-time lead.

Quins needed to hit back quickly and they did just that with two tries in six minutes.

First Londoner Worrincy cut back against the grain from Henry Paul's pass to score under the posts and then Randall went over from dummy half.

Rob Purdham added both conversions and suddenly Harlequins trailed by just two points.

It could have been even better for the hosts, but Haggerty spilled possession as he came on the crash ball just two yards from the line.

But they levelled the scores after 53 minutes through a Purdham penalty and went in front for the first time on the hour when Clubb rose highest to claim Orr's cross-kick.

Purdham slotted the conversion and former Cas player Orr was soon back in the action, slicing through the middle of the visitors' defence before rounding the full-back for a cracking try.

Once again Purdham was on target and he made it seven from seven after Howell and Haggerty added further tries for the hosts.

Ward went over after 78 minutes, with Paul adding the extras, as Harlequins romped clear to win a classic game of two halves.

Quins boss Brian McDermott:
"It wasn't down to me - the players had all the right things to say at half-time.

"We have a lot of good leaders in the dressing room and they knew what needed doing. To be honest I left halfway through the break and thought 'we've got this covered'."

Castleford coach Terry Matterson:
"I am dumbfounded by what happened. I probably need to get a copy of my half-time talk because I won't be using that again.

"I reckon I could have scored a treble in the second half - that is how poor our defence was.

"We are all embarrassed about it. In the second half it was just too easy for them and that is the most disappointing thing."

Harlequins RL: Wells, Clubb, Gafa, Howell, Sheriffe, Paul, Orr, Temata, Randall, Ward, Mbu, Worrincy, Purdham.
Replacements: Rinaldi, Haggerty, Melling, Grayshon.

Castleford: Donlan, Fletcher, Dixon, Shenton, Wainwright, Thackeray, Sherwin, Higgins, Henderson, Korkidas, Huby, Clayton, Lupton.
Replacements: Moore, Boyle, McGoldrick, Haberecht.

Referee: R Silverwood (Dewsbury)