Esmael Goncalves scored twice as St Mirren booked their place in the quarter-finals of the William Hill Scottish Cup.
The 21-year-old striker, on loan from Portuguese side Rio Ave, took his tally to four goals in three games as the Saints recorded their third victory in six days.
Goncalves headed home to break the deadlock four minutes after half-time and doubled the hosts' advantage seven minutes later.
"It's been a great week, we are starting to find that level of consistency that we were striving for," Lennon said. "I am delighted at the effort of the team and that they are finally getting the rewards for those efforts.
"Esmael was fantastic again today and he's only going to get better. He's had quite a baptism at the club and he's going to have a fantastic career."
St Johnstone manager Steve Lomas bemoaned his side's lack of firepower in front of goal following their cup exit.
Lomas' side passed up a host of chances before Goncalves' double and Lomas said: "We thought we had got over our Achilles heel in the last few games, we had looked clinical in our last two matches.
"I felt we should have went in at half-time 2-0 ahead. Craig Samson has made one wonderful save, that's what he's paid for though.
"That's the difference and the reason as to why we are not second in the league just now. The defending for the two goals was a shambles and cost us big time."