There were four minutes gone in the second half when Hoops defender Mikael Lustig fouled Mark Corcoran 20 yards from goal and Parkhead goalkeeper Fraser Forster had no chance when Staggies skipper Richard Brittain fired the free-kick high past him and into the net.
It looked like the Highland side would hold on for their first league win over the Glasgow giants but, in the third minute of added time, Commons pounced to tap the ball into the net from close range after County keeper Michael Fraser had spilled a shot from Hoops substitute Tony Watt, who had replaced Lustig.
The home side, who extended their unbeaten run to 37 games, might feel harshly done by and Celtic manager Neil Lennon celebrated the leveller with some gusto, as he now turns his attention to the first leg of their Champions League play-off against Helsingborg in Sweden on Tuesday night.
The Irishman will be hoping there were no more casualties from this hard-fought but entertaining encounter.
Lennon had 10 players missing for the trip to Dingwall in Dylan McGeouch (broken jaw), Daryl Murphy (hamstring), Gary Hooper (hamstring), Anthony Stokes (ankle), Mo Bangura (thigh), Rabiu Ibrahim (groin), Paddy McCourt (groin), Scott Brown (hip), James Forrest (groin) and Filip Twardzik (ankle).
That lengthy injury list meant Lennon had to reshuffle his side with Greece striker Georgios Samaras asked to lead the line supported by Commons, while starting with a back three of Lustig, Kelvin Wilson and Charlie Mulgrew.
County made three changes with midfielder Stuart Kettlewell returning from suspension and Rocco Quinn and Corcoran also coming in for Sam Morrow, Martin Scott and Paul Lawson, the latter two out injured.
Kettlewell should have scored for the home side in the ninth minute when defender Mark Fitzpatrick planted a cross from the left on to his head but he somehow missed the target from six yards out.
As County sensed some hesitancy in the Celtic defence, striker Colin McMenamin had the ball in the visitors' net but the offside flag had been raised long before the Staggies striker slipped the ball past Forster.
The champions announced their arrival in the game soon afterwards when midfielder Beram Kayal's lofted ball to the back post found wing-back Emilio Izaguirre, who knocked it back into the middle only for Samaras to head limply over the bar.
Parkhead midfielder Victor Wanyama then failed to get proper connection on a Commons corner and the ball bounced through to County keeper Fraser.
It was Celtic's turn to miss a great chance in the 25th minute when Samaras headed Charlie Mulgrew's long ball into the path of Commons giving him time to pick his spot from 10 yards, but Fraser made a good save with his legs.
As the game ebbed and flowed a 30-yard snap-shot from Ross County midfielder Iain Vigurs, after Wanyama had been muscled off the ball by Kettlewell, had Forster stretching high to his left to clutch out of the air, before Samaras failed to get on the end of another good cross from the energetic Izaguirre at the other end.
With 10 minutes of the first half remaining and Celtic on top, Wanyama headed a Commons corner off the bar before the home defence gratefully cleared the danger.
Brittain's free-kick four minutes after the break, after Lustig had fouled Corcoran 20 yards from goal, gave Forster no chance as it flew high past the big Geordie and into the top corner.
Two minutes later, with the ecstatic home support still celebrating, Samaras went down in the Ross County box after a challenge from Brittain but referee Craig Thomson ignored the penalty appeals.
Celtic had been clearly stung and when Commons fired in a powerful drive from 30 yards, Fraser made an unorthodox block with his knees.
In the 57th minute, after County defender Ross Tokely had clumsily fouled Commons 20 yards out, Mulgrew curled in a left-footed free-kick which clipped the bar.
Watt replaced Lustig with Wanyama moving back to defence as Lennon tried another route.
But in the 74th minute, as the Highland side broke, Corcoran's cross to the other side of the box was met on the volley by Quinn but his goal-bound effort was blocked by Mulgrew.
Celtic's desperation increased and Paul Slane made his top-team debut in the 78th minute when he replaced Kelvin Wilson, but as the Staggies broke again moments later, Brittain crashed a 30-yard shot off the bar with Forster beaten.
County had to defend desperately in the closing minutes as Celtic swarmed around their penalty area looking for the equaliser.
In the 88th minute Fraser made a great save from Samaras' close-range header, following a Mulgrew cross, and Kayal and Watt came close with efforts.
It seemed like County would hold out but Commons struck with seconds remaining to show why the Hoops are champions.