Premiership new boys West Ham had come into this game buoyed by the confidence of just one defeat in their opening three games that had already seen them notch up a win and a draw, too.
But Villa had also lost only once in their four previous matches and they had the added psychological edge of knowing that they had beaten the East Enders to the signature of Baros after Liverpool decided that he was surplus to requirements at Anfield.
And while all eyes were on the costly Czech, it was the barnstorming Harewood and his bustling team-mates who stole the show with a fabulous 4-0 victory that also saw Yossi Benayoun score his first goal for the club.
During a lively opening spell, Matthew Etherington, Paul Konchesky and even goal-shy Tomas Repka tested Thomas Sorensen from long range before another electrifying West Ham move saw Benayoun's curling 15-yarder saved by the Villa keeper.
It was only a matter of time until West Ham broke the deadlock and, sure enough, on 25 minutes Teddy Sheringham's defence-splitting, headed pass sent Harewood galloping clear and he coolly stroked the ball under the diving body of Sorensen from ten yards.
That was pure relief for the Hammers striker who had been hung out to dry for missing two sitters in his side's defeat against Bolton Wanderers last time out.
And as the half-hour mark approached, Harewood's rehabilitation continued when, with his back to goal, he toe-poked Anton Ferdinand's goalward header beyond the unsighted Sorensen after Etherington launched a well-flighted corner into the danger zone.
With a little more luck, Harewood might even have had a first-half hat-trick while, on the other hand, Villa trudged off at the break with just a Kevin Phillips mis-kick and a low James Milner shot to show for their opening 45 minutes work.
Shortly after the restart, Milner's speculative cross from the right wing rocked the far upright before agonisingly rolling along the goal-line and ricocheting off the near post only for Phillips to blast the loose ball into the side-netting.
That miss extinguished all hopes Villa had of staging a second-half recovery.
For as Hammers set about carrying on from where they had left off, Etherington's deep 50th-minute touchline free-kick was met at the far post by that man Harewood who gleefully claimed the match-ball with powerful angled, eight-yard shot.
Responding to East End chants asking him for the score, Baros finally woke from his slumber to unleash a couple of shots, but on a night when West Ham were superior in every department, Roy Carroll was equal to both efforts.
And by the time Benayoun turned Aaron Hughes inside out before slotting home in the 89th minute, rampant West Ham had already well and truly secured seventh spot in the Premiership.