A Christie header and an injury-time Greg Tansey strike were enough to spoil St Johnstone manager Tommy Wright's preparations for his side's Scottish Cup final date with Dundee United on Saturday.
St Johnstone dominated early possession and carved out the game's first clear opportunity when Michael O'Halloran stung the palms of Inverness goalkeeper Dean Brill with a 14th-minute shot.
But the home side improved as the half progressed. Midfielder Christie had a long-range effort whistle past Alan Mannus' post before heading straight into the St Johnstone goalkeeper's arms just past the midway point in the half.
Tansey also had a shot on target for Inverness with a strike from distance, but Mannus was equal to the challenge, gathering the ball comfortably.
The away side began the second half with added purpose and O'Halloran almost opened the scoring early on, only for Brill to tip his effort over the bar.
Caley Thistle responded with a driven shot by David Raven which Mannus turned past his bottom left post.
And just shy of the hour mark they got the opening goal that their superior possession merited. Mannus could not hold on to Graeme Shinnie's 59th-minute shot and 19-year-old Christie was on hand to head home from close range.
They should have extended their lead soon after when Christie played a ball over the top which fell to Aaron Doran who saw his effort scrambled clear following a collision between Mannus and Billy McKay.
Shinnie fizzed in another effort from range which Mannus turned behind for a corner, but the St Johnstone goalkeeper could do nothing about Tansey's injury-time effort.
A swift counter-attack from Caley Thistle in the first minute of stoppage time saw the ball crossed in by Danny Williams, but St Johnstone were unable to clear their lines.
Tansey cut inside to fire home, sealing fifth place in the league and helping Caley Thistle reach 57 points - their highest ever Scottish Premiership points tally.