The fiery Finn stormed up the tunnel after booting an advertising board as he was hooked with 20 minutes remaining of the 2-1 loss at Rugby Park.
He had endured a torrid day on a heavy pitch which was lucky to pass a pre-match inspection.
But even so, the former Lecce star looked more than a few pounds above his prime fighting weight and offered little of his old magic and even less in terms of graft.
Johnston, however, insists the 31-year-old was only showing frustration at the result.
He said: "Alexei is fine. The pitch was really heavy and there was talk of it being abandoned before the game. It's hard on the legs and you could see at the end both teams looked tired. It took its toll.
"But Alexei is just desperate to win. There's nothing wrong with that. At least he is showing he is passionate and cares that he wants to get a result.
"That's what we need - everyone trying their utmost to get the win so we avoid this dreaded play-off spot.''
The defeat leaves Killie just three points above 11th-placed Partick, but it looked so much more promising for the hosts after just four minutes when Robbie Muirhead put them ahead.
Perth keeper Allan Mannus could only parry a Kris Boyd strike and 18-year-old Muirhead was first to react to the loose ball.
However, St Johnstone levelled on 31 minutes when Frazer Wright darted to the near post to head home from Lee Croft's corner.
Then, two minutes before the break, a mirror image of the leveller lead to Saints' second when David Wotherspoon's delivery from the opposite side allowed Steven Anderson to poke home on the corner of the six-yard box.
"To lose two goals as cheaply as we did is really frustrating,'' said Johnston. "You have got to defend that better. Twice they have shown more desire to get in front of our players and that made the difference.''
St Johnstone now go into next Sunday's Scottish Cup semi-final showdown with Aberdeen on a high.
Boss Tommy Wright said: ''It was the perfect preparation for next week. The performance and result will give them confidence.
"Our away record has been really poor this season. That is only our fourth away win in the league.
"So I'm really pleased we have got another though. We have now got a few days off before we can concentrate fully on the semi-final.''
The win also marked skipper Dave Mackay's 200th appearance for the club but it was his defensive colleagues Wright and Anderson who proved to be the match-winners.
"We haven't scored enough goals from set plays,'' said the manager. "We get great deliveries from the likes of David Wotherspoon and Lee Croft but we haven't made the most of that this season.
"However Frazer Wright has done really well to get across his man for the first, while Ando's finish is just quality.''