In an exciting encounter at Upton Park, the powerful striker
fired a blistering opener inside the opening five minutes and then
added a second just 10 minutes later to leave the Hammers in poll
position and heading for their first victory of the season.
However, Villa dragged themselves back into the game with a goal just minutes before the break and netted twice in the space of nine second half minutes to complete a stunning comeback and leave the hosts facing a fourth successive defeat in the Barclaycard Premiership Reserve League South.
In his last official match in charge of the reserves before taking on his new role as Alan Pardew's First Team Coach, Kevin Keen was able to field a strong side, as Harewood partnered Carlton Cole up front, with England goalkeeper Robert Green continuing his progress between the sticks after injury.
Adding further experience in front of Green were defenders John Pantsil and Tyrone Mears, making their comebacks from knee and calf injuries respectively, while Northern Ireland international left-back George McCartney appeared in a Hammers shirt for the first time after recovering from a knee ligament injury sustained while with Sunderland last season.
Christian Dailly was the senior figure in midfield, with youngsters Tony Stokes, Kyel Reid and Hogan Ephraim adding youthful enthusiasm, although Stokes gave a sign of his potential by continuing to captain the side after his impressive performance against Arsenal's second string last week.
And it was Stokes who had the first goalscoring chance of the evening, as Cole's clipped cross from the left was nodded down by Ephraim into the six-yard box, where the skipper was on hand to toe-poke an effort goalbound. Goalkeeper Robert Olejnik only managed to palm the ball out to Harewood, who then saw his fierce effort from 12 yards out somehow blocked by a defender.
Just moments later, though, Harewood was celebrating his long-awaited first goal of the season, and in stunning style, as his 25-yard screamer flew past Olejnik into the top left hand corner of the net at the Centenary Stand end.
Three minutes later, Marlon should have made it two, but failed to connect with Reid's inch-perfect cross from just six yards out. However, on 16 minutes, he did double his tally, as a corner from the right was only cleared out to the edge of the penalty area and Mears fired in a low effort that was hooked into the net from close range by the Hammers striker.
Seconds later, Harewood almost completed a stunning quick-fire hat-trick with a clever flick from Reid's cross that sailed just past the post and, with Hammers surging forward at every opportunity, it appeared only a matter of time before a third goal would arrive.
However, after somehow managing to escape the opening half an hour with just the two goals conceded, it was Villa who hit back against the run of play, just two minutes before half-time, when a curling cross from the right caught the Hammers back-line flat-footed and striker Christian Kabeya ghosted in to nod the ball past Green.
The strike out of the blue clearly had a galvanising affect on Villa, who began the second half in determined mood and thought they had claimed an equaliser just seven minutes in, when striker Chris Sutton, recently signed from Celtic, climbed above Mears to head a free-kick past Green. Thankfully, though, referee Stretton spotted that the former England star had fouled his marker.
On 61 minutes, the impressive McCartney made way for youth team defender Lorcan Fitzgerald, while Villa replaced their scorer Kabeya with Adam McGurk and, just moments later, the two substitutes were involved in the incident that led to the visitors drawing level.
Fitzgerald was adjudged to have tripped McGurk just inside the box, and midfielder Craig Gardner sent Green the wrong way with his spot kick.
Further changes were then made, as Jack Collison came on for John Pantsil, and with the game opening up following the departure of our two full-backs, Villa took full advantage to net what turned out to be the winner.
Another of Martin O'Neill's former Celtic stars, Didier Agathe, gained possession on the right and sent over a deep cross that McGurk forced home at the far post to make it 3-2 and earn the plaudits as a genuine super-sub.
Harewood was denied the chance to rescue a point with a hat-trick goal after being replaced by Junior Stanislas on 79 minutes - perhaps with an eye on Sunday's mouth-watering trip to White Hart Lane.
The unfortunate Hammers reserves may have trudged off the pitch disappointed after failing to secure their first win of the campaign, but Alan Pardew will have headed away from Upton Park boosted by the possibility that last season's top goalscorer may well have received the confidence boost in front of goal that will hopefully transmit to the Premiership this weekend…
Hammers: Green; Pantsil (Collison 76), Mears, Ngala, McCartney
(Fitzgerald 61); Ephraim, Stokes, Dailly, Reid; Harewood (Stanislas
79), Cole. Unused: Blackmore, Jeffery.
Villa: Oleknik; Green, Cahill, Bouma, Bridges; Agathe, Osbourne, Gardner, Berger (Stieber 81); Kabeya (McGurk 64), Sutton (Lund 74). Unused: Henderson.
SEE MARLON'S GOALS AND HIGHLIGHTS OF THE MATCH TOMORROW, EXCLUSIVELY ON WHUTV...
3 - Cole races down the left and sends in a deep cross to the far post that is nodded down by Ephraim to Stokes, whose toe-poke is blocked by the goalkeeper, with the follow up effort from Harewood somehow cleared by a defender.
4 - GOAL! Harewood cracks a stunning strike from 25 yards into top left-hand corner of the net. West Ham United 1 Aston Villa 0.
7 - Reid cuts free on the left and delivers an inch-perfect cross that shaves the head of Harewood on the edge of the six yard box and flies out for a goal-kick.
13 - Berger's shot from the edge of the penalty area flies just wide of the post.
16 - GOAL! A corner from the right is met by Dailly, whose header is cleared off the line to the edge of the box, where Mears fires in a shot that is flicked home by Harewood. West Ham United 2 Aston Villa 0.
17 - Reid's cross from the left is met by Harewood, whose clever flick flies just wide.
23 - Pantsil's pass into the channel finds Harewood, who fires a first time shot just wide of the target.
31 - Sutton breaks clear in the penalty area but drags a cross-shot wide of the target.
39 - Sutton almost releases Kabeya in the box but Pantsil gets across to clear.
43 - GOAL. Villa pull one back as Paul Green's cross drops behind the defence and the unmarked Kabeya nods past Robert Green from six yards out. West Ham United 1 Aston Villa 1.
Half-time: West Ham United 2 Aston Villa 1
52 - Sutton heads a deep free-kick past Green from six yards out but the goal is ruled out after the striker is adjudged to have fouled Mears.
55 - McCartney's cross from the left is only cleared to the edge of the box, from where Stokes sends a dipping volley just inches wide of the post.
56 - Osbourne booked for a foul on Ephraim.
61 - Substitution for West Ham United, Fitzgerald on for McCartney.
64 - Substitution for Aston Villa, McGurk on for Kabeya.
65 - GOAL. After Fitzgerald's foul on fellow substitute McGurk, referee Stretton points to the spot and Gardner steps up to convert the penalty and level the scores. West Ham United 2 Aston Villa 2.
66 - Substitution for West Ham United, Collison on for Pantsil.
72 - Robert Green does well to hold on to a deflected 25-yard shot from Cahill.
74 - GOAL. Villa turn the match on its head as a deep cross to the far post is stabbed home by substitute McGurk. West Ham United 2 Aston Villa 3.
74 - Substitution for Aston Villa, Lund on for Sutton.
79 - Substitution for West Ham United, Stanislas on for Harewood.
81 - Substitution for Aston Villa, Stieber on for Berger.
82 - Ephraim's cross from the right is headed just wide by Stokes from eight yards out.
89 - Stokes fires high over the bar from 20 yards out as Hammers search desperately for an equaliser.
90 - Green gets down to superbly tip a low effort from Gardner round the post for a corner.
90 - Green comes to the rescue again with a stunning full-length save to keep out Stieber's snapshot volley.
Full-time: West Ham United 2 Aston Villa 3.