The Crusaders have 41 points and moved into seventh position, one place outside the playoffs, and still require other results to go their way.
Champions New South Wales Waratahs are in sixth place on 42 points, but play the 13th-placed Cheetahs later on Saturday and can end the Crusaders' hopes with a bonus-point win in Bloemfontein.
Carter was making just his fourth start this season in his preferred flyhalf position and has slowly come back into form in the last two weeks after a sputtering final Super Rugby campaign.
The Blues' season effectively ended months ago and with a host of injuries to their squad, coach John Kirwan gave several fringe players their opportunity to try and press their Super Rugby credentials ahead of next season.
They began promisingly enough with Ihaia West slotting two early penalties, but the Crusaders then scored 17 unanswered points in the first half with tries to Nemani Nadolo and Luke Romano while Carter converted both and added a penalty.
Nadolo's breathtaking try was created by Carter's vision with the flyhalf kicking across field and the Fiji international outjumped Ben Lam, grabbed the ball with one hand, lost it, then gained control again as he fell over the line to score.
Without injured All Blacks props Tony Woodcock and Charlie Faumuina, the Blues were overpowered at the scrum with referee Chris Pollock awarding a penalty try to the Crusaders in a scrappy second half.
Matt Todd scored the bonus point try after more forward dominance while Carter added another penalty and two more conversions before Lam scored a consolation try for the Blues with five minutes remaining. – Reuters
Original source: Crusaders maintain slim play-off hopes