When Tomas Cvancara stretched his neck and planted a header on Craig Gordon's crossbar an hour into this exhilarating clash of the champions and the wannabe champions, a sense of shock swept around Tynecastle.

Cvancara? Was he still out there? You could have been forgiven for thinking not. For an hour he'd been little more than a keen if ill-fitting presence in the Celtic attack.

His lack of goal threat was hardly a surprise given he has scored just three times in the 43 games he had played before this one. His lack of impact was no great sensation either given he hadn't played a competitive minute since late November.

The fact he was still on the pitch was a little odd because the game had passed him by, but that header showed there was life in the new boy.

More life than Hearts had bargained for. Minutes later, he tore away down the left, leaving Craig Halkett trailing behind. His delivery to Yang Hyun-jun was precise and against the flow of the game Celtic were back in front.

Tynecastle rubbed its eyes and then girded its loins. In those seconds, a compelling game became a total belter; thrilling, controversial, exhausting and invigorating.

Goals, aggravation, a red card that infuriated the visitors and opened a door for the hosts, a toe-to-toe fight that went to the wire.

It wasn't so much the bitter cold that caused the shivers at Tynecastle, it was the mad drama of the clash, the intensity and edge-of-the-seat fury of it all.

Hearts were stunned by the sucker punch from Yang, but these guys are made of stern stuff.

All season long there's been questions asked of them and their capacity to keep going, to keep threatening to rip up the established order of things in Scotland.

Could they beat the Old Firm? Well, yes. Four times out of four leading into Sunday. Could they find themselves again after a mini-slump in the autumn? Yes, they could. Who'll be leading the league at Christmas? Er, Hearts.

Who'll be leading the league in late January? Er, Hearts. In two recent games they have played with 10 men versus 11 for inordinate amounts of time and yet won both of those matches.

And now this test. Not against a demoralised Brendan Rodgers Celtic or a slapstick Wilfried Nancy Celtic, but a Celtic coached by a living Celtic saint.

To add spice they were without three totems of their team, Lawrence Shankland, Cammy Devlin and Beni Baningime.

Yes, Celtic were missing key men too, but removing those Hearts players was like removing vital organs. Could they survive? Another examination of their mettle.

Had they wanted to, they could have felt sorry for themselves at 1-0 and particularly at 2-1, they could have bemoaned the fantastic chances they had spurned, one from Claudio Braga and two from Alexandros Kyziridis. You thought of Shankland each time. Had he been on the end of them...

They could have looked around and moped that three architects of their success this season weren't there to help them now. They could have buckled, but didn't.

Celtic have played them three times this season and haven't won yet. At 1-0 and 2-1, and with Hearts missing their important leaders, this was Celtic's opportunity.

They'll go back to the red for Auston Trusty, but the bottom line is Celtic gave Hearts their best shot and have now dropped to third. The bottom line, also, is a depleted team looked Celtic in the eye and did not blink.

Their gap over Celtic remains at six but only four over Rangers, the shark circling the waters at the top, their teeth restored under Danny Rohl.

Rangers have come from chaos, humiliation and fury and have moved into serious contention.

It seems completely incongruous a club the size of Rangers, its life spent under a gigantic microscope, could possibly move quietly into contention, but that's the reality.

It only seems like five minutes ago since the boos at Ibrox could be heard in all corners of the country, where laughter was the dominant noise. Now, relatively speaking, we hear the sound of purring from that club.

This league is one of the greatest of our times; impossible to call but oh so easy to enjoy.

Celtic folk will feel they should still be locked together with Rangers on points and would be had it not been for that red card, a rarity for them in domestic football.

They will be incensed about the decision to send off Trusty for the denial of an obvious goalscoring opportunity when leading 2-1. Was it all that obvious? Martin O'Neill thought no. Derek McInnes thought yes. Funny, that.

It did change things, though. Trusty had gone just 10 minutes when Braga had his chance to level it; point blank and a goal to all the world. Kasper Schmeichel denied him. Only six minutes remained but, actually, there were another eight on top. The temptation was to cheer when the board went up.

The equaliser sent Tynecastle into an advanced state of delirium. Just like the first time, the source of Celtic's problems was their remarkable inability to deal with deliveries into their box.

Along with their angst about the red card some honesty about their defending should form part of their analysis. When Oisin McEntee nodded down at the back post, Braga smashed it home and sent Celtic back down the road in pain.

This league has a way to run. Any one of the top three could win it and any one of Falkirk and Motherwell could have a say in deciding who does because, on their day, they're capable of taking points off the sides above them.

That's what makes this season so intoxicating; so much jeopardy, so much unpredictability and so many teams who have come to the party.

Celtic thought they had Hearts on Sunday. If they focus solely on the red card then they're missing the point - the Jambos, it must be obvious to all, are not getting the jitters.