The Croatian found the net for the first time in a month in a late 2-1 win over Sunderland at Goodison Park, scoring soon after Marouane Fellaini had equalised Adam Johnson's first strike for the Black Cats.
It was far from the 27-year-old's best game but by scoring his first for a month, having entered October on the back of four goals in five matches, he may have rediscovered his touch.
Naismith, who played alongside Jelavic at Rangers, knows the benefit an in-form striker can have.
"It makes a huge difference. He has not scored in his last few games and he'll have be disappointed with that," said the Scot.
"He's not had many great chances in the game but the one that came his way he was composed and he put it away in the corner and that is why he has such a big reputation.
"Going forward Fellaini has probably been our most prolific and even Kevin Mirallas, in the last few games, has been very direct and arguably our most influential player.
"It is down to the quality we have in the squad. We are happy with the boys we've got and that is why we are pushing for the top spots."
Jelavic pounced in the 79th minute, swooping on Fellaini's backheel through the legs of John O'Shea to dispatch the winner past Simon Mignolet.
Just three minutes earlier Fellaini had drilled home to cancel out Johnson, who volleyed home his maiden goal for the club he joined in the summer and Sunderland's first in eight hours 54 minutes of football.
The win kept Everton in fourth place and manager David Moyes was pleased to see his main striker back among the goals.
"He looked delighted (when he scored) because he didn't have a good game," said the Scot.
"But I can tell you of a lot of centre-forwards who don't have good games and score - we can live with that.
"I didn't want to take our goalscorer off, especially when you are a goal down, because you want to try to find a way and we hoped something might drop to him.
"I am sure that will help him and hopefully we will start to see a run of goals from him again.
"I don't think we found him in the box or he didn't find enough space for us to get him the ball.
"But people who are centre-forwards will tell you they lose confidence when they don't score goals and regain it when they do.
"So it was good to see him and Felli scoring again. They are the people who we rely on a lot for goals and they came up trumps.
"Fellaini has proved this season he is a really important player for us.
"He has great chest control, he has lovely soft feet and he can play.
"When we needed him to drop back with 15 minutes to go he can play deeper as well."
The only downside to the day was when Mirallas limped off on the half-hour with a hamstring problem. He will have a scan to assess the damage.
"Every time he has been on the pitch for us he's looked a threat," said Moyes of his £6million summer signing.
"I don't think it's too bad but he'll have to have it scanned."
Sunderland, having ended their goalscoring drought, looked as though they would bring to an end an 11-year stretch without a victory against Everton.
Johnson paid back some of his £10million transfer fee with a smart volley but Sunderland needed to take more of their chances and manager Martin O'Neill left Merseyside frustrated.
"That will help Adam's confidence. He put in a very strong performance, particularly in the first half," he said.
"It was a good performance by Johnson, Stephane Sessegnon was outstanding for long periods and I am disappointed we didn't see it through for any of the points.
"With 14 minutes left we could have got three and we didn't get any.
"There was great spirit among the players and that was epitomised by the performance."
Everton later confirmed on their official Twitter account that Mirallas would not be joining up with the Belgium squad for their friendly against Romania on Wednesday.