Hammers had probed and pressured the Villa defence incessantly for 45 minutes before the teenage Defoe scored his first senior goal at Upton Park, a brilliant right-footed volley from just inside the penalty area that found the bottom far corner of the net at the Bobby Moore Stand end.
It was the least Glenn Roeder's side deserved after dominating for long periods following a badly conceded goal headed home by Dion Dublin inside the first minute.
David James, facing the club he left in the summer, miscued his clearance and the ball landed at the feet of Steve Stone, whose right wing cross was met by Dublin, who soared above Tomas Repka 12 yards out.
Apart from another Dublin header towards the end of the first half which he did very well to keep out from under the upright, the West Ham keeper had precious little else to do.
Although Hammers hardly threatened themselves in a low key first half - Paolo Di Canio forcing one save of note from keeper Peter Enckelman - it was one-way traffic after the break.
There was much more urgency about West Ham, who showed two changes from the side that had lost at Sunderland on Saturday. Nigel Winterburn relegated the unlucky Scott Minto to the subs' bench but a groin injury saw Paul Kitson make way for Di Canio, who had recovered from a hamstring strain.
The Italian should have marked his return with at least one goal and could have had a hat-trick in a frantic five minute spell midway through the second half. His first two shots on target were blocked by Steve Staunton and the legs of Enckelman but Di Canio was left cursing himself after seeing his weak 68th minute penalty easily saved by the Finnish keeper
It was Defoe, always lively even if no clear chances came his way, who won the spot kick when he was tripped by Staunton. Di Canio tried an audacious penalty similar to the one that succeeded at Liverpool on the openikng day - but this time he underhit a tame effort that Enckelman had no trouble gathering low to his right.
Di Canio has only missed two penalties in his time at the Club and the last time was just over two years ago...against David James of Aston Villa!
Having earlier been booked for furiously smashing the ball into the Chicken Run boards after another decision went against him, Upton Park held its breath sensing the Italian could explode in a fit of fury after seeing his penalty saved.
Instead, Paolo kept his composure and the skipper played a major part in driving Hammers further forward in a sustained attempt to grab the equaliser their second half onslaught had so richly deserved.
Di Canio set up Don Hutchison for a far-post volley that, once again, was blocked by desperate Villa defenders, while Trevor Sinclair saw two chances slip agonisingly wide of either post as Hammers turned up the heat.
Just when it looked as though time had run out, up popped Defoe to net the third Premiership goal of his career to ensure this match ended 1-1 for the third consecutive season.
It was the least Hamnmers deserved.
Minute-by-minute:
1 - GOAL. An absolute disastrous start for the Hammers, as David James' poor clearance from a back-pass falls to Stone on the right, who sends a left-footed cross into the box where Dublin is waiting to out-jump Repka and send a looping header past his former Villa team-mate after just 52 seconds. West Ham 0 Aston Villa 1.
3 - Hendrie's shot from the edge of the box takes a deflection off Dublin, almost deceiving James before dropping just wide of the post.
8 - Sinclair runs on to Cole's cross-field past and beats Wright to the ball before Enckleman clears. From the resulting cross, Defoe's header is then well saved by the Finnish goalkeeper.
9 - Stone booked for foul on Winterburn.
22 - After Hammers fail to clear a long free-kick, Dublin volleys just wide from the edge of the area.
23 - Defoe does well to control James' long kick upfield, teeing the ball up for Di Canio, whose fierce drive from the edge of the area stings the palms of Enckleman.
38 - Winterburn booked for encroachment at a free-kick.
39 - Merson's free-kick from the edge of the area is deflected just wide for a corner. From the resulting centre, Dublin pulls away from his marker Repka and heads the ball towards the top corner before James somehow claws it away with the help of post and crossbar.
Added time: 2 minutes.
Half-time: West Ham United 0 Aston Villa 1.
Second half:
46 - Substitution for Aston Villa, Samuel replaces Delaney.
48 - Di Canio's intelligent free-kick sets up Carrick on the edge of the area but the midfielder's low drive is deflected away for a corner.
52 - Di Canio booked for unsporting behaviour.
58 - Sinclair's dangerous cross is almost met by Defoe but Mellberg clears for a corner.
61 - Sinclair's deep cross is brought down brilliantly by Di Canio but the Italian's shot is blocked by Mellberg in the six-yard box.
64 - Hammers miss their best chance of the game so far when Hutchison cuts the ball back and Di Canio arrives to control the ball before seeing his shot blocked by Enckleman.
65 - Defoe gains possession on the right and skips past Staunton, who hauls him down. Referee Dean takes his time before pointing to the spot.
66 - Di Canio steps up to take the spot-kick but his weak effort is easily held by Enckleman.
68 - Substitution for Aston Villa, Vassell replaces Merson.
70 - Another glorious chance goes begging as Cole releases Sinclair though the middle with an inch-perfect pass, only for Trevor to show too much to Enckleman and then toe-poke his effort wide.
78 - Dailly meets Di Canio's corner with his head and then follows up a loose ball but is denied by another save from Enckleman.
81 - After Defoe's excellent turn on the halfway-line, Mellberg's back-pass is shot and Sinclair latches on, only to poke his effort just wide of the far post.
89 - Yet another great opportunity is wasted as Di Canio's deep cross drops perfectly at the far post for Hutchison - who somehow scuffs his volley along the six-yard box before Staunton clears.
Added-time: 3 minutes.
90 - GOAL! The Goal-den boy Jermain Defoe saves the day as he latches on to Hutchison's hopeful ball over the Villa defence and fires a first time volley past the despairing dive of Enckleman, rescuing a point for the Hammers - the least they deserve. West Ham United 1 Aston Villa 1.
Full-time: West Ham United 1 Aston Villa 1.