Dana McClelland prevented Hokowhitu from getting a shot away on their first free kick.
But Whanganui struggled to contain Hokowhitu's attacking style of charging straight up the middle or long passes over the top, while in turn trying to play that way themselves instead of sticking to their tried-and-true.
A strong strike had the home team up early, which was followed by their second goal just before halftime.
"We said to the girls all week, 'this is what they do, you have to take responsibility'," said Calvert.
"They love it when we tell them how brilliant they are, but when you give them the harder chats, they didn't respond at halftime."
Hokowhitu then pressed their advantage after the break for 3-0, before Whanganui started to turn momentum as their opposition got tired.
Captain Vanya Apiata Hodgkinson scored her fourth goal in five games from a header off a corner in the 66th minute, and then Whanganui had the better of the final 10 minutes, with the Hokowhitu keeper making three big saves on the way to being named their player of the day.
"Just couldn't find that second goal which would have made things interesting," said Calvert.
The coach said he liked that his squad, so often the whipping girls for the stronger teams in the past two seasons, walked off the park saying they let themselves down, rather than feeling they couldn't compete.
"I can't wait for Hokowhitu to come back to us, because we've seen how they go.
"We are far ahead of where people thought we'd be. We've shown we can take on any team in this league."
Hokowhitu have now checked out six points clear of the rest of the pack, which still includes Whanganui among four teams that have similar results above the winless Feilding United – Whanganui's record is now 1-1-3 with 11 goals scored, eight conceded.
"What's going to end up happening, every single game, it's going to be fine lines that make the difference," said Calvert.
"What was great as well, we saw people who have come to watch home games, and on Sunday it was not just family members, but it was people who were travelling to watch us."
Whanganui start the second round this Sunday with another Memorial Park game against defending champions PN Marist, who they surprised with a 2-2 draw on opening day in early April.