Celtic 3 (Armstrong 24; Campagnaro [OG] 26; Guidetti 90+3) Inter 3 (Shaqiri 4; Palacio 13, 45).
The Swedish striker stepped off the subs’ bench to net his first goal in 11 appearances for Ronny Deila’s side and keep their hopes of further progress alive.
On an evening when they needed to be firing on all cylinders, Celtic’s hopes looked to have been fatally derailed by a malfunction of their normally most reliable component.
Craig Gordon, whose exceptional goalkeeping was the biggest single factor in them reaching this stage of the tournament, endured an uncharacteristically wretched evening. Celtic found themselves two goals behind to Inter after just 13 minutes with Gordon at fault for the first of them by Xherdan Shaqiri.
Stuart Armstrong hauled Celtic level before half an hour had elapsed, scoring one and forcing an own goal from the rattled Italians. But another howler from Gordon allowed Rodrigo Palacio to plunder his second goal just before half time.
It looked to have given Inter a lead to take into next Thursday’s second leg at San Siro before Guidetti’s late intervention.
After creating a cacophonous Champions League-style atmosphere in the build-up, the home support had the wind taken out of their sails by their team’s calamitous start to the contest.
Just as they had in their previous knock-out tie with Italian opposition, against Juventus in the last 16 of the Champions League two years ago, Celtic conceded the opening goal within the opening four minutes. It came from a rare error of judgment by Gordon. His outstanding performances in the group stage of this tournament often compensated for the defensive vulnerability in front of him. But the perfectionist in Gordon would not be pleased with his part in Inter’s breakthrough. Although left exposed by Zdravko Kuzmanovic’s ball over the top of the defence which picked out Shaqiri’s run, he was less than convincing as he clawed the Swiss striker’s initial shot straight back into his path. The former Bayern Munich player seized upon the loose ball and calmly guided it into the net.
It was the kind of start Deila’s men would have dreaded and, to a man, they appeared rattled. It would get worse before it got better. Slack play from Virgil van Dijk presented Kuzmanovic with Inter’s next chance which he wastefully scooped over. But the visitors’ second was only delayed until the 13th minute.
Gordon was more effective in dealing with a Shaqiri shot this time as he turned the ball behind. But from the corner, taken by Kuzmanovic, Celtic were all over the place defensively. Shaqiri helped the ball back into the area where it broke off Van Dijk for Palacio to drive a firm, low shot beyond Gordon.
When Gordon then had to make a decent stop to deny Mauro Icardi, Celtic appeared on the verge of total collapse.
But they gradually recovered a measure of composure before displaying considerable resilience to battle their way back. It was breathless stuff as Celtic stunned Inter with two goals in as many minutes to level matters.
Armstrong will certainly never forget his home debut for Celtic. The midfielder sparked the revival in the 24th minute with one of the perfectly-timed runs into the penalty area which became his trademark at Dundee United. It allowed him to get on the end of a well-judged cutback from Adam Matthews and slot a low shot past the left hand of Inter keeper Juan Pablo Carrizo into the corner of the net.
The grateful celebrations of the Celtic fans had hardly subsided when they were greeting an equaliser. Stefan Johansen was the provider from the right this time, the Norwegian’s cross causing panic in the Inter defence. Under pressure from Armstrong, full-back Hugo Campagnaro bundled the ball into his own net.
The momentum was firmly with Celtic at this stage and it required a brave save by Carrizo at the feet of Gary Mackay-Steven to prevent the winger joining his fellow new boy on the scoresheet. Inter looked every bit as uncertain at the back as Celtic but unfortunately for the hosts it was they who were punished again for another mistake by Gordon just before the interval.
Gary Medel’s long through pass from his own half was intended for Palacio but was overhit as the ball ran into the penalty area. Gordon advanced for what should have been a routine interception but instead the ball slipped from his grasp and into the stride of Palacio who coolly stroked it into the far corner of the net.
The tempo of the contest subsided to the merely frantic after the break. Inter confounded the stereotype of Italian sides being content to sit on a lead, pouring forward at every opportunity. Palacio, on the hunt for a hat-trick, forced a smart save from Gordon who dived to his right to keep out a curling shot.
Celtic’s response was a stinging long-range effort from Nir Bitton which flashed just wide. Mackay-Steven should have done better when he found himself one-on-one with Carrizo, sending in a tame shot which the goalkeeper blocked with his left foot. Leigh Griffiths was equally wasteful, shooting straight at Carrizo from close range after being set up by Johansen.
Guidetti replaced Griffiths with 15 minutes remaining and his impact was stunning. With the seconds ticking down in stoppage time, he got on the end of a long ball from Emilio Izaguirre and thumped a superb volley high into the net.
There was time for one more Inter attack and a degree of redemption for Gordon who, in the final piece of action before the final whistle, dived brilliantly to his left to keep out Shaqiri’s free-kick.
CELTIC: Gordon; Matthews (Ambrose 81), van Dijk, Denayer, Izaguirre; Bitton, Brown; Armstrong (Henderson 75), Johansen, Mackay-Steven; Griffiths (Guidetti 75). SUBS NOT USED: Zaluska, McGregor, Wakaso, Scepovic. BOOKED: van Dijk, Johansen, Henderson.
INTER: Carrizo; Campagnaro, Ranocchia, Juan Jesus, Santon; Medel, Guarin, Kuzmanovic (Dodo 79); Icardi (Kovacic 75), Shaqiri, Palacio. SUBS NOT USED: Handanovic, Vidic, Obi, Puscas, Hernanes. BOOKED: Santon, Campagnaro, Shaqiri.
REF: Istvan Vad