Manager Brendan Rodgers praised Reo Hatate as a "different animal" after Celtic kicked off their Scottish Premiership title defense with a commanding win over Kilmarnock.
The Japanese midfielder, whose performance was hindered by injuries last season, showcased his best form by scoring an early goal, helping Celtic top the table at the end of the opening weekend.
In a match marked by a title flag unfurling and a celebratory atmosphere, Celtic continued their strong performance with additional goals from Liam Scales, Nicolas Kuhn, and Anthony Ralston, who scored for the first time in two and a half years.
Hatate, a key player under Ange Postecoglou, struggled to maintain his previous levels of play after Rodgers took over.
"I've got to be honest, the player I've seen over the course of pre-season is the player I expected to see last season," the Celtic boss said.
"He never really got to the level he wanted to consistently last season. Now I'm seeing a different animal.
"His mentality, his focus, the quality of his game. When he's playing against bigger opponents, he's shown he can play to a high level.
"He's an outstanding footballer and he'll be very important for us this season."
Kyogo Furuhashi came close for Celtic before Reo Hatate opened the scoring.
A mix-up in the Kilmarnock defense saw Lewis Mayo lose possession to Greg Taylor, who then found Hatate on the edge of the box.
Hatate drilled his shot into the bottom corner past Robby McCrorie.
Kilmarnock's best chance came just before the half-hour mark when Kyle Vassell outmuscled Cameron Carter-Vickers and set up Matty Kennedy in the Celtic box.
However, Kennedy's shot went straight at Kasper Schmeichel, who had a trouble-free debut.
Celtic doubled their lead just before halftime with an unexpected goal from centre-back Liam Scales. Scales beat his marker to head home Matt O'Riley's cross, making it 2-0.
Nicolas Kuhn, who struggled to adjust to life in Glasgow last season, scored Celtic's third.
Kyogo made a superb pass to Kuhn, who worked his way into the box and scored via a deflection off Mayo.
Celtic had several more chances to score, and while Kyogo did find the net with 10 minutes remaining, his goal was ruled out for offside.
However, Anthony Ralston celebrated a rare goal just before full-time, squeezing the ball past McCrorie after Kyogo's initial shot was saved.