Striker Didier Drogba showed just why Chelsea made him their record signing with two goals in two minutes to give his side an easy 2-0 win over Middlesbrough on Tuesday.
The victory extended their lead at the top of the English Premier League to seven points after big rivals Arsenal were held 1-1 at home to Manchester City.
"Obviously he had an operation which takes a long time to come back from," Clarke told a news conference. "In recent games he has shown signs of being back to his best. Tonight was a great boost for his confidence."
The Ivory Coast international collected an excellent Frank Lampard pass on 15 minutes before easily turning centre back Gareth Southgate to slot past goalkeeper Mark Schwarzer.
Two minutes later the pair combined again when Drogba headed in Lampard's low flighted free kick.
After missing six weeks with the injury Drogba has spent much of the season coming on from the bench with manager Jose Mourinho preferring Icelandic international Eidur Gudjohnsen as the pivot in his three-man attack.
However, Mourinho has brought Drogba into the action increasingly early in recent weeks and after a display of such power combined with craft, Gudjohnsen could struggle to regain his place.
The league leaders should have scored several more with winger Damien Duff guilty of a poor first-half miss.
He also rattled the bar with a fierce effort on 57 minutes while Joe Cole, Lampard, full back Paulo Ferreira and Dutch dribbler Arjen Robben with a trademark run and shot all went close.
Chelsea have won all four matches in the busy holiday period and despite Arsenal and Manchester United only drawing on Tuesday, Clarke said the players remained focused.
"At the moment we are out in front and enjoying it but the only thing that matters is being in front in May," Clarke said.
Middlesbrough manager and former Manchester United number two Steve McClaren said of Chelsea: "At the present time you have got to say they are favourites. But if they get injuries to key players then Arsenal and Manchester United are always waiting but it is Chelsea's to lose."