St Mirren would have taken ninth with victory at the Caledonian Stadium.
They have another chance but must beat title-chasing Rangers on Monday to jump above Caley Thistle, and earn an extra £70,000 in prize-money.
Defender Proctor saw red for a professional foul on former Inverness striker Craig Dargo early in the second half, but St Mirren failed to make their man advantage count despite peppering Michael Fraser's goal with a flurry of late shots.
The teams remain two points apart, with the season now over for Inverness who were held to a goalless draw for the first time in the campaign.
Managers Craig Brewster and Gus MacPherson each made two team changes.
Dennis Wyness and Russell Duncan came into Brewster's Inverness side at the expense of Ian Black and Rory McAllister, while MacPherson called Stephen O'Donnell and Hugh Murray into his line-up in place of Franco Miranda and Jim Hamilton.
Proctor was booked after just eight seconds for a heavy challenge on Dargo, who left the Highland club last summer.
From the free-kick, Ryan McCay's shot was dealt with comfortably by home goalkeeper Fraser.
Don Cowie shot wastefully over the St Mirren bar from Dougie Imrie's cross in the early stages before Mark Howard made a comfortable save from Imrie.
Dargo, looking to double his tally for the season after scoring just once for the Buddies, failed to get on the end of David Barron's dangerous cross.
Wyness, who could make a summer move to St Mirren once he becomes a free agent, then failed to find the target with a headed chance.
Inverness threatened again when Cowie's shot was turned away for a corner, which they could not capitalise on.
O'Donnell was the next to threaten an opening goal but Fraser made sure of the save, and at the other end Howard showed safe hands to thwart Wyness.
Dargo had been prolific in his spell with Inverness and great things were expected of him at St Mirren, however he was getting little joy on his return to the Caledonian Stadium and was caught offside as he looked to penetrate the home defence.
His replacement at Inverness, Marius Niculae, went close for the hosts with one opportunity which hit the post and soon afterwards shot over the St Mirren bar, but neither side could muster a goal before the break.
Billy Mehmet and O'Donnell caused Inverness some concern with early strikes in the second half for St Mirren, but Mehmet cleared the bar and O'Donnell's shot from a narrow angle was parried by Fraser.
Niculae then headed wide from Barry Wilson's corner as the hosts looked to reassert themselves, and Cowie was the next man to miss the target.
Proctor had avoided a red card for his early challenge on Dargo, but a professional foul on the same man saw him ordered off in the 54th minute, with Andy Dorman firing over from the free-kick which followed.
Barron saw yellow for a crude challenge on Imrie, before Wyness received a standing ovation to mark the end of his final appearance for the club as Brewster withdrew him in the 57th minute and brought on midfielder Black to give the 10 men a more solid look.
Home defender Ross Tokely almost headed an own goal from Wilson's next corner, and soon afterwards went into referee Eddie Smith's book for fouling Dargo.
Niculae departed in the 72nd minute, with Graham Bayne taking over as the lone striker, while St Mirren brought Hamilton on for Gary Mason to give them extra firepower.
O'Donnell became the fourth player cautioned when Smith punished his foul on Imrie.
Wilson's involvement ended when he was taken off and fellow midfielder Richie Hart, who will join Ross County in the summer, was afforded a final appearance for Inverness.
Barron for the visitors had the next chance when Fraser had to tip his shot past the post, and Dargo went for a late winner against his former club but put his shot wide.