Saints captain Dave Mackay saw a penalty saved by Radoslav Cierzniak at the end of the first half and it was United who eventually took the lead through John Rankin – only for Murray Davidson to hit back swiftly and secure a point.
Saints were the first to show as David Wotherspoon sent a shot wide in the fourth minute but United created a chance of their own soon afterwards – Chris Erskine calling home goalkeeper Alan Mannus into action.
The dangerous Nadir Ciftci fired a warning shot in the 19th minute when he saw an effort rebound off the post but the hosts were creating the better of the chances as Mackay and Danny Swanson both failed to convert inviting openings.
In first half injury time, Saints were awarded a penalty when Callum Morris clumsily brought down Michael O’Halloran – only for Cierzniak to produce an excellent stop from Mackay’s spot-kick.
The visiting goalkeeper was alert again to prevent Davidson’s header from opening the scoring in the second half and Wotherspoon should have worked him once more on the hour-mark after a slick pass from Swanson.
In the 68th minute, United snatched the lead when Robbie Muirhead crossed and Rankin located the top corner with an impressive header from the centre of the penalty area.
The industrious Swanson was the architect of Saints’ equaliser – picking out Davidson with an accurate cross that the midfielder did well to divert into the bottom corner from 12 yards to seal the draw.
The result means Inverness will definitely finish third and qualify for European football for next season – Dundee United hold sway in fourth place with a slightly better goal difference than Saints.