John Hartson has called for perspective after Celtic's first defeat by Rangers at Parkhead in over nine years gave the visitors a Ladbrokes Premiership title boost.
Nikola Katic's second-half header, after an Odsonne Edouard goal levelled Ryan Kent's opener on Sunday, took the Light Blues to within two points of the Hoops at the top of the table with a game in hand going into the winter break.
It was the first Rangers victory at Celtic Park since October 2010 but Hartson – who played for Celtic between 2001 and 2006 – noted the champions' current domination of Scottish football as they strive for a ninth-successive title while having beat the Ibrox side 1-0 in the Betfred Cup final at Hampden Park earlier in the month.
"I genuinely felt we had a title race this season. Rangers showed in the final that they are a real threat to Celtic," he told TalkSport.
"It is certainly not going to be a stroll in the park like it has been for the previous eight seasons if you like.
"Whenever Celtic get beat, because they have been so dominant – they got beat twice last season by Rangers, one of them was when the league was already won – there is always an outcry and everyone goes a little bit over the top.
"You have to put a bit of perspective on the win yesterday.
"Yes, Rangers were better. They played ever so well, they got the tactics right, they had players who caused Celtic an awful lot of problems and Celtic didn't pass the ball well.
"They are closing the gap, they have got some very good players but Celtic missed a penalty and had two opportunities cleared off the line. Big moments in the game.
"But Celtic have played Rangers three time this season and beaten them twice.
"Celtic are going for their 15th title in the last 19 years (20) and have won the previous 10 trophies on offer.
"So yes, Rangers deserved the win, they played really well but crisis...or there is a turn in where the league is going to go – there is still another 17 or 18 games to play this season in the league.
"There is always a massive outcry, people go over the top, they get carried away.
"Rangers were better yesterday, it was a fantastic performance, good luck to them. But let's not over react because Celtic lost one game."
Rangers boss Steven Gerrard's post-match celebrations were enthusiastic but Hartson expressed surprise that the former Liverpool and England captain had not shaken the hand of Celtic boss Neil Lennon and assistant John Kennedy in the traditional manner.
He said: "He was obviously absolutely thrilled by the win. It is not easy to win at Celtic Park.
"I thought the handshake was slightly wrong. I thought he just slapped Neil's hand and John Kennedy's hand and walked away.
"I thought Stevie would have shook the hands, man to man and looked them in the eye, but he didn't,
it was almost like a high five, a slap and walked away.
"It is not a criticism. He was obviously delighted to get the three points, his team played very well but that was the only thing – I was a bit surprised he didn't shake the guys' hands."