Hughes took charge of Caledonian Thistle this week and his new side's failure to break down the Buddies left them seven points adrift of Scottish Premiership leaders Celtic.
Caley keeper Dean Brill was quickly forced into action as he kept out Jason Naismith's drive before saving Steven Thompson's shot in a lively opening.
Marc McAusland's close-range effort was blocked as St Mirren continued to search for an opener and Thompson's shot looked goal-bound until it was tipped onto the post by Brill.
McAusland went close again when he nodded over, but Inverness then created a rare opportunity as Aaron Doran fired wide.
The Buddies began the second-half brightly and Thompson's effort from a difficult angle flew over, but Doran spurned another sight of goal with a wayward shot.
Inverness were starting to apply some pressure and Billy McKay nodded at Marian Kello before Marley Watkins was inches away from an opener with a header that struck the post.
But second-placed Caley endured a late scare as McGregor appealed in vain for a penalty after he tangled with Brill in the box.