Jim Smith admitted his Derby team enjoyed "a lucky break" with the last-ditch equaliser that denied Chelsea one-day leadership. But Gianluca Vialli gambled harder and more dubiously and no amount of suave spin-doctoring afterwards could conceal Chelsea's disappointment.

Vialli would say the means, mass manipulation of his squad at Pride Park, justifies the ends - overhauling Manchester United, starting on Wednesday at Old Trafford. But Vialli stands accused here, like a general, of seeing the broad front but overlooking the troops on the ground.

Chelsea's manager is playing the long game - "there's no hurry, the Premiership doesn't finish tomorrow," he intoned - but questions about his seasonal strategy are discouraged largely because they involve squad rotation, a subject on which Vialli's patience has long been exhausted. But this dreaded R-word and its dangers were still being whispered at Pride Park.

Vialli left out six players who started in Wednesday's uplifting victory over Aston Villa and changed formation not once but twice, the second seeing Gianfranco Zola again substituted and looking as despondent trudging off as he had against Villa.

Chelsea's manager could be said to be taking liberties with his players and, by implication, with certain opponents. In which case Derby answered arrogance with Dean Sturridge's late equaliser.

"We should have got the three points; we were a bit unlucky," argued Vialli, with some justification. Yet Derby deserved something from Smith's devil-may-care triple substitution 11 minutes from time and his shrewd view that Chelsea's defence would succumb to penalty-area pressure. That thinking almost vindicated Vialli's switch to three central defenders.

Derby's defence was tormented by Tore Andre Flo, whose latest goal adorned a performance that was near-faultless. Seldom has English football seen a tall forward of such touch, turning ability and pace as this seemingly awkward Norwegian. Yet this was only Flo's fifth start in the Premiership this season. It was the first for the teenager Jody Morris, whose magnificent chipped pass was merely one impressive moment in a midfield performance of extraordinary maturity.

Vialli mused afterwards that this young Englishman "probably would be a regular in all the "other" teams in the Premiership". But such is the difficulty of second-guessing this manager that the local boy may not get a look in on Wednesday. Neither can the captain Dennis Wise be sure of a place, even if there is the sentimental tug of his 32nd birthday. United tend to bring out the troublesome worst in Wise, who begins his third suspension next Saturday.

Smith did talk of "rotation" but only in terms of Chelsea's positional switches and movement. "Frightening," he called it, and fear indeed seemed to spread to his side once Vialli's team had levelled with Flo's goal. Gustavo Poyet's strike only four minutes later was beautifully created - by Flo - but should have been saved by Mart Poom, who dived too late.

Chelsea's defence was in even greater disarray a minute from the end when one substitute, Kevin Harper, crossed and another, Sturridge, forced the ball home after Paulo Wanchope's jab. Derby's first goal was equally untidy, a deflection by Bernard Lambourde into his own net, but Horacio Carbonari's vicious free-kick almost demanded reward.

Derby have much quality of their own, notably the returning Italian Francesco Baiano and the one-time Chelsea left-back Tony Dorigo who, at 32, outshone Graeme Le Saux. They have met all top eight teams barring Middlesbrough, leaving Smith well placed to assess the title contest. Already, he thinks, "it will go to the wire, between Chelsea, Arsenal, United and Villa" - although not necessarily in that order.

"Villa have added players since we played them, and Arsenal have that ability to dig in and get results. The difference with Chelsea is that they're so good going forward - a bit like United.

"We felt that if we got enough balls into their area we could cause Chelsea problems, but it's not that easy because you can't get the ball off them."

Derby County: Poom, Carbonari (Sturridge 79), Powell, Dorigo, Wanchope, Delap, Bohinen (Schnoor 79), Laursen, Prior, Eranio, Baiano (Harper 79). Subs Not Used: Hoult, Elliot. Booked: Powell, Carbonari, Wanchope. Goals: Carbonari 26, Sturridge 90.

Chelsea: De Goey, Leboeuf, Goldbaek (Petrescu 46), Poyet, Wise, Duberry, Le Saux, Flo, Lambourde, Zola (Nicholls 89), Morris (Babayaro 89). Subs Not Used: Hitchcock, Di Matteo. Booked: Flo. Goals: Flo 55, Poyet 59.

Referee: P Jones (Loughborough).