The Chairboys dominated the first half and looked to be cruising through after goals by Paul Hayes and Alfie Mawson opened up a healthy aggregate lead.
The Pilgrims fought back in the second half but Ainsworth’s players managed to withstand the onslaught, winning 5-3 across the two legs, and will now meet Southend on May 23 for a place in League One next season.
Ainsworth said: “You don’t get lucky in these two games, you earn what you get and after two tough legs I want to pay tribute to my players because I felt they handled the situation extremely well.
“I thought the mental side was the most important thing today after what happened down at Home Park, with Plymouth ending in the ascendency.
“I had to get the mental side right before the game because the physical side is there.
“We played really well in the first half, it was a complete performance which got us a lead that was a mountain to climb for Plymouth in the second half.
“But again the scare came – they scored and worked a good goal, but I thought we defended really well.
“I had players out there who weren’t 100 per cent fit but that’s what I’ve got here – I’ve got characters who will play through anything for me.”
Wycombe went ahead on the night when Plymouth goalkeeper Luke McCormick failed to deal with Sam Saunders’ corner and Hayes hooked in from close range.
McCormick was at fault again when Mawson beat him to Joe Jacobson’s corner to nod in the Chairboys’ second, with Ryan Brunt’s back-heel the best Plymouth could muster as they bowed out.
Plymouth boss John Sheridan said: “I’m just really disappointed in how we performed in the first half given the situation we were in.
“I stuck with my team and went with the same formation – I’ve kept faith in them but the first half was probably the worst performance from any team I’ve managed.
“We’re in a position where we’re going into the play-offs and we know the importance of it and we just did not get going.
“That’s five goals we’ve conceded in two games from set-plays and we’d been good throughout the season dealing with them.
“In the second half, we had a go at it and tried to get something, we put three subs on at the same time and I thought in the second half their keeper’s made some good saves.
“We’re all down at the moment – it’s hard to take the defeat because it’s a great chance gone missing.”