The wee Hibees had won four and drawn two in the CAS Elite Under-18s League going into the penultimate game before the split.
The Buddies beat Aberdeen 4-2 in their last fixture on April 30 and with Hibs posting a 5-3 victory at Kilmarnock, the encounter was sure to produce goals.
With Rangers’ 2-1 win against Aberdeen earlier on Tuesday taking them top, victory for Hibs would have seen them leapfrog the Gers while three points for the Buddies would take them second.
Gareth Evans and Eddie May made two changes to the side that had won in Ayrshire with Innes Lawson, who opened his account in the previous game, replacing Murray Aiken in central midfield and Brodie Watt starting on the right flank in place of Josh Currie.
After a one-sided first-half, the teams went in at the break with the hosts three goals to the good and although Hibs fought back in the second half with Connor Young netting another brace to take him into double figures for the campaign, the Buddies scored again to end any hopes of a comeback.
Hibs now face Rangers at the Hibernian Training Centre on May 7 in their final pre-split game, while St Mirren travel to Kilmarnock, who beat Hearts 4-3 at the Oriam yesterday.
Team: Murray Johnson; Jacob Blaney, Jayden Fairley, Mack Weir, Oscar MacIntyre; Brodie Watt, Innes Lawson, Robbie Hamilton, Josh O’Connor; Connor Young, Ethan Laidlaw. Subs: Josh Blair, Ben Reilly, Reece Holden, Freddie Wylie.