Match ends, Celtic 2, St. Johnstone 0.
Giorgios Giakoumakis revelled in the "amazing feeling" of his first Celtic goal as Ange Postecoglou's men overcame stubborn St Johnstone for a fourth straight win.
The Greece striker marked his first start with the opener and Celtic finally made sure of a deserved home victory with Josip Juranovic's penalty.
Postecoglou's side stay fourth in the Scottish Premiership and are four points behind leaders Rangers, who returned to the top with Sunday's win at St Mirren.
St Johnstone's second successive defeat drops last season's cup double winners to 10th, two points above second-bottom Dundee.
"It's an amazing feeling and something I was missing so much. For sure it will help my confidence," said Giakoumakis, a summer signing from Dutch club VVV Venlo.
"I am not a patient guy, so it was a bit difficult waiting to regain fitness. But I worked hard and I'm getting fitter day by day."
Giakoumakis was unleashed from the start after impressing in the Europa League win over Ferencvaros, his third outing off the bench.
But the 26-year-old and Celtic were superbly marshalled by St Johnstone until a lapse from Callum Booth undid all the visitors' diligent defending.
Juranovic's hopeful shot from distance took a looping deflection into the box, where Booth missed his attempted clearance, allowing Anthony Ralston to square for Giakoumakis to volley past Zander Clark.
It brought relief for the hosts and dejection for St Johnstone, who had welcomed back defensive lynchpin Liam Gordon from injury for a first appearance since August.
Bar a Callum McGregor drive stopped by Clark's outstretched leg, the hosts had struggled to penetrate until Giakoumakis struck.
Kyogo Furushashi, deployed wide right to accommodate the Greek forward in the central striker role, was a peripheral presence but Jota on the opposite flank was Celtic's liveliest performer.
St Johnstone came out with fresh impetus after the break, Jamie McCart heading over from a corner and Cammy MacPherson slicing high and wide.
Celtic quickly reasserted control, and McGregor had a drive deflected inches wide, but the hosts were restricted to few clear-cut chances until the closing stages.
The clinching goal arrived when Jota and Kyogo combined and the Japan forward - moved centrally after Giakoumakas went off - was caught by Gordon just inside the box. Juranovic sent Clark the wrong way from the penalty spot.
Tom Rogic and McGregor had drives batted away by Clark, either side of a shot off the post by substitute Mikey Johnston, as St Johnstone avoided further damage.
Man of the match - Jota
What did we learn?
Celtic have their key men back and are continuing to build momentum after a chaotic start to Ange Postecoglou's tenure.
Giakoumakis' goal will bolster the striker's confidence as he strives for full fitness, and Croatia defender Juranovic showed his quality after a four-game injury absence.
While Celtic have now won three league matches in a row, St Johnstone have suffered three three defeats and netted just one goal in four.
Davidson's side will rue the defensive lapses at both goals, but were solid for the most part while lacking threat at the other end.
Gordon's return to the heart of defence offers hope of a revival, with three of the Perth men's next four league fixtures at home.
What did they say?
Celtic manager Ange Postecoglou: "It was a game where you know you're not going to get a lot of space in and around the penalty box and they're never going to open up.
"It was important we maintained our discipline, moved the ball around and were clinical when the chance came. We didn't allow St Johnstone to be a threat, and we could have scored a couple more at the end."
St Johnstone manager Callum Davidson: "Callum Booth misjudged it. It's not like him. It was a long-range shot and if we deal with that, then we don't concede.
"I am not blaming Callum. I don't think Celtic had many chances in the first half but we got punished then the game becomes a little bit harder for us."
Both sides are in Premiership action against Edinburgh opposition on Wednesday night (19:45 BST), with Celtic away to Hibernian and St Johnstone hosting Hearts.
- 20Carter-VickersBooked at 77mins
- 8FuruhashiSubstituted forAbadaat 81'minutes
- 7GiakoumakisSubstituted forJohnstonat 61'minutes
- 17Neves FilipeSubstituted forAjetiat 86'minutes
- 25AmbroseBooked at 79mins
- 6GordonBooked at 79mins
- 18MacPhersonBooked at 29mins
- 13BrysonBooked at 55mins
- 14MiddletonSubstituted forCrawfordat 63'minutes
- 9KaneBooked at 77minsSubstituted forVertainenat 85'minutes
- 10WotherspoonSubstituted forMayat 70'minutes
- Nick Walsh
- Shots on Target
Second Half ends, Celtic 2, St. Johnstone 0.
Attempt missed. Josip Juranovic (Celtic) left footed shot from the left side of the box misses to the right. Assisted by Tomas Rogic.
Attempt saved. Callum McGregor (Celtic) left footed shot from outside the box is saved in the top centre of the goal.
Attempt blocked. Michael Johnston (Celtic) left footed shot from the left side of the box is blocked. Assisted by Josip Juranovic.
Corner, St. Johnstone. Conceded by Cameron Carter-Vickers.
Attempt blocked. Stevie May (St. Johnstone) right footed shot from the right side of the box is blocked. Assisted by Cameron MacPherson.
Attempt missed. Liel Abada (Celtic) left footed shot from the centre of the box is too high. Assisted by Albian Ajeti.
Michael Johnston (Celtic) hits the right post with a right footed shot from the left side of the box. Assisted by David Turnbull.
Dangerous play by Carl Starfelt (Celtic).
Eetu Vertainen (St. Johnstone) wins a free kick in the defensive half.
Substitution, Celtic. Albian Ajeti replaces Jota.
Substitution, St. Johnstone. Eetu Vertainen replaces Christopher Kane.
Attempt missed. Cameron Carter-Vickers (Celtic) header from very close range misses to the right. Assisted by David Turnbull with a cross following a corner.
Corner, Celtic. Conceded by Callum Booth.
Attempt missed. Anthony Ralston (Celtic) right footed shot from the centre of the box misses to the right. Assisted by Jota with a cross following a corner.
Corner, Celtic. Conceded by Zander Clark.
Attempt saved. Michael Johnston (Celtic) right footed shot from the centre of the box is saved in the bottom right corner. Assisted by Jota.
Substitution, Celtic. Liel Abada replaces Kyogo Furuhashi.
Goal! Celtic 2, St. Johnstone 0. Josip Juranovic (Celtic) converts the penalty with a right footed shot to the bottom right corner.
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