Yang Hyun-Jun was "sensational in every aspect of the game" as he helped Celtic to a 3-1 win over 10-man Motherwell, according to Martin O'Neill.
Celtic started brightly, with an Alex Oxlade-Chamberlain effort turned onto the post, but they fell behind to Elijah Just's goal in the 32nd minute. However, Yang profited from a defensive blunder just six minutes later to level the score.
Motherwell's Emmanuel Longelo then received a straight red card for holding in the penalty area, and Tomas Cvancara turned in the resulting penalty to give Celtic the lead.
Yang then netted his second of the game in the 79th minute, securing three points which boosted Celtic's Scottish Premiership title hopes whilst seemingly ending Motherwell's outside chance.
It was a vital win for O'Neill's side, as Hearts are now just two points clear of the Bhoys at the top of the table after slumping to a 1-0 defeat to Kilmarnock later on Saturday.
And O'Neill gave credit to Yang, who had been deemed surplus to requirements at Celtic Park at the start of the season before a move to Birmingham City fell through.
"He was sensational," O'Neill said. "Sensational in every aspect of the game.
"Going forward, with the goals he scored, the energy and the willingness to work back, it was a monumental performance by him."
Celtic have now won 13 points from losing positions in the league this season, more than any other team.
And they were well deserving of their victory, as they produced 2.1 expected goals (xG) from their 13 shots, getting six of those on target, while hitting the woodwork twice.
"It's a big win, and to come from behind and play in the manner that we did. Naturally, I'm delighted with the performance," O'Neill told BBC Scotland.
"Where it comes in the scheme of things, I genuinely don't know. But, to play against Motherwell, who are a fine, fine footballing team and fight back with all the things that were mounting up for us, like injuries, the team have found spirit.
"But spirit alone won't do it for you, and they played brilliantly. That's a delight."