Shane Duffy thundered home a header on his debut as Celtic thrashed Ross County to stay in touch at the top of the Scottish Premiership.

Second-half goals from Duffy, fellow centre-back Kristoffer Ajer, and substitute Patryk Klimala completed Celtic’s biggest win of the season.

They remain six points behind leaders Rangers with two games in hand.

County, with around 300 home fans watching on in a test event for the return of supporters, hit the post either side of half-time but had no answer to Celtic’s attacking power.

Celtic’s switch to a back three allowed them to play to their strengths and pair Edouard and Ajeti up front for the first time. The effect was devastating, although it came with a couple of nervy moments at the other end.

County couldn’t take advantage, with Celtic goalkeeper Vasilis Barkas impressing. The Greek got the faintest of fingertips to an Iain Vigurs free-kick, sending it on to the upright, and saved smartly from a near-post Ross Stewart header.

Duffy, meanwhile, was relived to see the offside flag raised after being blindsided by Billy Mckay, who latched on to a long ball. But by the time County striker Oli Shaw struck the woodwork in the second half, the hosts had been obliterated.

Celtic were 2-0 up inside 20 minutes, with both goals a gift. Coll Donaldson clipped Edouard, allowing the striker to send Ross Laidlaw the wrong way from the spot, and then Ajeti lashed in from six yards after the hosts made a mess of trying to clear a free-kick. It’s now three goals in three league outings for the Swiss international.

Vasilis again denied Stewart at the start of the second half, before Neil Lennon’s side turned on the afterburners. Duffy’s thumping header from a Callum McGregor corner put the result beyond doubt on the hour and Ajer soon made it four from Olivier Ntcham’s low delivery.

Klimala, having failed to convert from close range after wonderful build-up play from Edouard, made amends by rounding off the champions’ third straight league win after a botched Vigurs backpass.

Man of the match – Odsonne Edouard

What did we learn?

Celtic need to stick with a 3-5-2. Lennon admitted pre-match it is his favoured formation, with only his strikers’ lack of fitness preventing him deploying it until now. Edouard dovetailed well with Ajeti, whose predatory instincts again came to the fore.

And while it can leave them vulnerable in defence, particularly down the flanks where Jeremie Frimpong and James Forrest marauded forward, it is a trade-off worth taking. Duffy slotted in seamlessly to the back three, gave notice of his goal threat, and will only improve when his match fitness is up to scratch.

County, meanwhile, must eradicate the lapses at the back. They remain in the top six, but have the league’s second worst defensive record with 11 goals conceded.

Stuart Kettlewell’s side offered plenty of enterprising forward play, only to have it undermined by losing soft goals.

What did they say?

Ross County manager Stuart Kettlewell: “It was a crazy game. We were the dominant team in the first half and created the best opportunities by far in open play. We got done by a free-kick and penalty.

“The big differences came in the 18-yard boxes, we didn’t defend well enough. Outwith that, we created so many chances and had to be more ruthless.”

Celtic manager Neil Lennon: “First half we were a little bit off it, which was to be expected with a few changes and different system. As the game went on we looked far more powerful.

“Our goalkeeper made some great saves as well – which is something we’ll have to look at – but I’m delighted for him and it was an all-round good team performance in the end.”

What’s next?

Celtic will be eyeing another win when they travel to coronavirus-hit St Mirren on Wednesday, while Ross County are away to St Johnstone on Saturday.