Hibs scored twice in the opening five minutes to claim maximum points but failed to build on a great start.
Colin Nish cleverly chipped Chris Smith after the goalkeeper had made a mess of kicking away a pass-back.
Merouane Zemmama then smashed home a wonderful strike from long range as Hibs threatened to run riot.
But St Mirren dominated the second half and Hibs keeper Andy McNeil made four great saves to deny David Barron and Will Haining – three times.
Hibs needed a win to stay in the hunt for a Uefa Cup place but failed to make up ground on third-placed Motherwell, who were surprise winners at Celtic Park.
Nish was gifted the opening goal after a blunder from goalkeeper Smith, who fluffed a kicked clearance straight to the Hibs striker.
The centre forward netted his fourth goal since joining the Easter Road side in January with a sublime chip over the retreating Smith from 25 yards out.
Zemmama extended the lead just 60 seconds later with a thumping shot from 30 yards which flew past the bewildered Smith and into the top corner of the net.
Smith got his gloves dirty for the first time when he saved another strike from the menacing Moroccan midfielder.
Steven Fletcher had the ball in the net again in the 12th minute but was adjudged to have strayed into an offside position to head in Thierry Gathuessi’s cross.
Following a St Mirren corner, Zemmama broke with speed and trickery and found Nish in a promising position but Smith raced from his line and managed to stop the striker’s flicked finish when a goal looked certain.
The visitors were under siege for much of the first half but the game fell rather flat after half an hour and the visitors managed to spring one or two attacks.
Buddies striker Craig Dargo sent a header wide from seven yards on 37 minutes and McNeil saved from a long distance effort from Andy Dorman.
St Mirren made a bright start to the second half but went close to losing another goal when Alan Reid headed against his own crossbar from an inswinging Zemmama corner.
On 58 minutes, Barron cracked a sweet volley on target but McNeil made a terrific save to push it over the crossbar.
The Hibs keeper then made another two fabulous stops to deny St Mirren defender Haining.
The defender thought his header had crossed the line but McNeil clawed it away then acrobatically kept out a powerful volley.
St Mirren substitute Stewart Kean and Haining tested McNeil in the final minute but the under-21 international again made impressive saves.
Hibs: McNeil, Gathuessi, Hogg (Chisholm 61), Canning, Zarabi, Zemmama, Murray, Rankin, Shiels (Stevenson 76), Fletcher, Nish (Donaldson 83). Subs Not Used: Ma-Kalambay, Kerr, Benjelloun, Morais.
St Mirren: Smith, Reid (Kean 80), Haining, Potter, Maxwell, Murray (Brittain 50), Dorman, Brady, Barron, Mehmet, Dargo (Hamilton 76). Subs Not Used: Mathers, Corcoran, Docherty, McGinn.
Referee: S Finnie.