Modest Lorient, long a bogey side for PSG, were 2-0 up at half-time and were only pegged back by Ibrahimovic's late second strike, from the penalty spot, on his French league debut.
PSG, also boasting expensive new signings Ezequiel Lavezzi and Marco Verratti, were brought back down to earth with a bump after five minutes when defender Maxwell diverted a left-wing cross into his own net.
A shocked Parc des Princes could then hardly believe their eyes when Jeremy Aliadiere ghosted through the entire PSG defence after a quick break to easily score a second on the stroke of halftime.
Alain Traore's well-placed free-kick almost embarrassed PSG further but for an expert save by Nicolas Douchez.
Coach Carlo Ancelotti, whose Qatari-backed team of highly paid players were beaten to the title by unheralded Montpellier last term, was open-mouthed in indignation at the break with the PSG forwards showing no cohesion.
Former AC Milan striker Ibrahimovic hit the post and then pulled one back midway through the second half with a trademark goal of strength and flair before Jeremy Menez shot over when it looked easier to score.
The equaliser finally came in the 90th minute after Gregory Bourillon was sent off for a foul on Blaise Matuidi and Ibrahimovic slammed in the spot-kick.
Montpellier, with top scorer Olivier Giroud now at Arsenal, drew 1-1 with Toulouse in the season opener on Friday.
DELIGHTFUL CURLER
Bordeaux, the 2009 champions who endured an insipid season last term, started this one in good form with a 3-2 win at Evian on Saturday with Poland midfielder Ludovic Obraniak opening the scoring with a delightful curler.
Playmaker Yoann Gourcuff flopped for Olympique Lyon last term but began the new campaign with a bang, netting after 15 minutes in a 1-0 win at 10-man Rennes.
Lille, champions two campaigns ago, began life without Chelsea's new wing wonder Eden Hazard by claiming a 2-1 victory at Saint-Etienne where Benoit Pedretti scored the late winner.
There were contrasting starts for promoted duo Bastia and Troyes with the former coming from behind to win 3-2 at Sochaux but the latter losing 1-0 at home to Valenciennes.
AJ Ajaccio, who somehow stayed up last term after seeming adrift, won 1-0 at Nice despite being reduced to 10 men for the second half while Nancy beat Brest 1-0 in eastern France thanks to Yohan Mollo's added time winner.
