That target had looked highly unlikely a few months ago as Tommy Wright's men propped up the Ladbrokes Premiership table.
But a seven-game unbeaten run has transformed their campaign and they are now just three points behind fifth-placed Livingston, with Hendry's strikes adding 13 points to the Saints tally.
"Callum is there to score goals," said Wright after the 1-0 victory. "You always worry whether he'll last in the final 15 minutes of the game but he came up with a goal again.
"He took his goal well and as I've said on numerous occasions if he keeps working hard he's got a big future ahead of him. But Callum has a lot of hard work ahead of him."
Wright revealed he had warned his players that one chance could settle it at windswept McDiarmid.
"It was a poor game, you can't butter it up any other way," he said. "But ultimately it's about getting results at this stage of the season.
"We said at half-time that it was a game which would be won by one bit of quality and we produced it. It was a great cross from Drey (Wright) and a great finish from Callum.
"If it had finished 0-0 I don't think we could have argued, but we are three points behind Livi now so we have given ourselves a chance."
It was a bitter pill for Livi manager Gary Holt to swallow.
"When you see the conditions and the underfoot conditions you just don't want to make a mistake and give away a goal that costs you," he said. "It wasn't conducive to football and I don't think there was much played. It was percentage football and St Johnstone had to play the same.
"We play a risk and reward game but it wasn't a day for it.
"We had the better chances in the game but we have to defend better, the ball was sent wide and we didn't stop the cross, you can't defend like that.
"Whether it was offside or not I don't know, but you can't come here, do all that work and leave with nothing.
"It was a good finish but from our point of view it was poor defending.
"The manner of the defeat is the disappointing thing."