Tommy Wright felt St Johnstone should have put the 2-1 win to bed long before the end as Ross County made their Scottish Cup tie a cliffhanger.
Michael O'Halloran and James McFadden had the Cup holders comfortably ahead but County bounced back through Jake Jervis, who also missed a good chance.
Saints missed a host of chances to settle the tie long before the end.
"We should have been well ahead in the game," said Wright. "We were at 2-0 but we should have got another goal."
|St Johnstone manager Tommy Wright on Cup chances|
|"The Cup's all about on the day and getting that bit of good fortune and we know that."|
He told BBC Scotland: "We had enough opportunities to do that, and then we started the second half really slack and allowed them back in the game.
"They put us under a bit of pressure but we defended well, but in that period in the second half we had some clear-cut chances where we could have put the game to bed. We didn't.
"Whilst there's only one goal in it the opposition always have a chance, but overall I think we deserved our victory.
"We felt after last week their [County] confidence would probably be high even though they lost the game, so we made sure we started the game well and we did and two good goals put us in total command."
St Johnstone lifted the trophy for the first time in May with a 2-0 victory over Dundee United, but Wright admits it will be a big ask to repeat the feat.
"On any given day we can beat anybody, that's what we've always tried to base ourselves on," he said. "If we're hard to beat we always think we've enough quality in the side.
"The Cup's all about on the day and getting that bit of good fortune and we know that as well, but we're pleased we've come through this round.
"We'll look forward to the draw and see who we get in the next round."