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.
Inverness Caledonian Thistle struck with the last kick of the game as the Highlanders claimed a dramatic 2-2 draw in a controversial encounter against Hearts.
Eighteen-year-old Conor Pepper rescued a draw after Terry Butcher's men appeared dead and buried at the break - two goals down and a man down following a tempestuous first period.
Arvydas Novikovas had given the hosts the lead on 15 minutes, curling past Ryan Esson, before John Sutton doubled Hearts' lead after a debatable penalty award.
Richie Foran was shown a red card on the stroke of half-time, prompting the fury of Butcher, but Caley were handed a lifeline with a penalty of their own, Andrew Shinnie netting. Pepper then sparked wild celebrations among the visitors deep into injury time.
Jamie Murphy struck twice as Motherwell claimed their first three-points of the season with 2-1 victory over Kilmarnock at Rugby Park.
Murphy opened the scoring after 11 minutes when he drove at the home defence and slotted the ball beyond Cammy Bell.
Gary Harkins levelled on the half-hour, but within five minutes Murphy was racing on to Michael Higdon's excellent through-ball before rounding Bell and rolling the ball into the net.
Pat Fenlon's new-look Hibernian claimed their first win of the SPL season with a 2-1 success at St Mirren.
A goal in either half from Leigh Griffiths gave them a two-goal lead but the Edinburgh side had to withstand a fightback from Saints, who could not add to Steven Thompson's goal.
However, the hosts were made to rue their penalty miss, with Paul McGowan's first-half spot-kick saved by Hibernian goalkeeper Ben Williams.
Aberdeen got their first win of the new season after beating St Johnstone 2-1.
Issac Osbourne and Jonny Hayes provided the goals but the score does not come close to describing the visitors' superiority, particularly in a second half where Aberdeen controlled the play in the St Johnstone half and created numerous chances.
Nigel Hasselbaink added a late consolation for the hosts, but the defeat from the season home opener leaves St Johnstone with only a point from their first three SPL games.
- Fraser Forster
- Michael Fraser
- Mikael Lustig
- Mark Corcoran