Emerton outfoxed the Foxes back four during a lively 70-minute showing as Town claimed a 2-1 victory in their final pre-season game at Sixfields.
It was the perfect preparation for Saturday’s Sky Bet League Two curtain-raiser at York City and Boothroyd now has decisions to make on who he wants in his squad for that game.
The manager handed chances to seven trialists in the game against Leicester, but was particularly impressed with Emerton and Michael Spillane, who were the only two to start.
“He’s terrific,” said Boothroyd of Emerton. “I was really very impressed with him.
“I’m going to have a think about all the guys we had on trial and I’ll make some calls and decide what I’m going to do.
“Hopefully, with a bit of luck, we’ll have another couple in (by Saturday).”
And on Spillane, who excelled at centre-back and in central midfield, he added: “He was excellent.
“I know he can play at centre-back, at right-back and in midfield, he’s a good character and I’ve got to weigh it all up and make the right decisions now.”
Cobblers’ win came courtesy of a Lee Collins strike and a Sean St Ledger own goal and Boothroyd was pleased with the workout his side got against a strong Leicester side.
“Overall, it was a really, really good game for us,” he said.
“The result doesn’t mean anything and the biggest thing is that both teams have escaped injury-free.
“We go into our respective seasons having had a really good workout on a Tuesday night.”