The Crusaders fell short in their bid to dislodge the Chiefs from top of the New Zealand conference despite defeating the Hurricanes 25-17 in their final round-robin match.
The seven-time Super Rugby champions had already secured their berth in the play-offs but needed a bonus-point victory in Christchurch to have a chance of pipping the Chiefs to first place in the conference.
However, they were unable to get the four tries they needed against the already eliminated Hurricanes in a match which saw both sides each cross three times apiece.
The Crusaders went over through Zac Guildford, Andy Ellis and Tom Marshall, with Dan Carter adding the crucial extra points with two penalties and two conversions, while the Hurricanes responded with tries from Victor Vito, Brad Shields and Julian Savea, only one of which was converted by Andre Taylor.
The result leaves the Crusaders in fourth place in the overall standings on 60 points, one behind the Chiefs, and they will now wait to see who their opponents will be in the first round of the play-offs.
The Rebels were 24 points behind at half-time and looked destined to slump to another loss when they trailed by 20 with a little over 20 minutes remaining.
But with O'Connor at the centre of nearly every attacking surge in his final game for the club, the Rebels scored four tries in the closing stages to finish their Super Rugby season on a high.
The Highlanders didn't trail for the first 79 minutes of the contest, with Bryce Hegarty scoring the winning try right at the death to help the Rebels register their fifth win of the season and complete their most successful campaign in Super Rugby to date.