Jackie McNamara hopes his Dundee United team's first win of the season will give his players a boost to their confidence and help them climb the Scottish Premiership table.
"Once we got the second and third goals, everybody was a bit more relaxed and expansive on the ball," he said after
"I'm delighted for the lads. They've been working hard.
"It's just been getting the confidence, getting that first win."
While the home team could celebrate hammering their Tayside rivals, for St Johnstone it was their first domestic defeat of the season.
Goals by Keith Watson, David Goodwillie - his first since returning to Tannadice - and Gary Mackay-Steven had United in control at the break.
And, when Stuart Armstrong made the most of Mackay-Steven's lay-off in 53 minutes, the Terrors were four goals to the good.
"There may be a few people shocked at that result, but I knew we were capable of doing it," said McNamara.
"I said last week after the performance at Hibs that, if we could take our chances, we would cause anybody problems.
"It's just getting that consistency. I still think we can play a lot better than we did today. Our passing was a bit slack at times, but the pleasing thing was we had an end product.
"The players who started today have set the standard. The good thing is we have a strong bench and there are other players sitting in the stand.
"It hopefully gives the boys a bit of confidence that they can go and express themselves properly."
The Tannadice boss, describing the Perth Saints as "a physical and well-organised team", added that the key to the win was pulling the St Johnstone players about the pitch.
"We knew if we moved their centre-halfs around and their full-backs, we would get in behind them and fortunately that proved to be the case," he said.