Wycombe had the lead over their Premier League opponents before three late goals settled the game for Spurs.
Ainsworth said: "The scoreline is probably not a reflection of the game although they were fantastic at the end - I am flattered they had to put some big names on to get in front. We looked tired, we have given everything and there is no disgrace from our boys, really proud - we will take a lot of heart from this.
"We have only trained one day in the last eight, that has hampered things, missing a couple of key players but no excuses - for 85 minutes we were well in the game, the third and fourth goals kill us. We go again, it's not going to be the FA Cup but I am determined to stay in the Championship.
"We have to take positives out of tonight, their second string is good enough to compete in the Premier League, never mind the Championship. Son, Kane, Hojbjerg, some really good players coming on.
"I am going to tell my boys they are good enough to stay in the Championship."