But Smith admits Australia are looking to balance the side with an all-rounder - John Hastings or Marcus Stoinis - meaning one of the strike bowlers will be receiving an unwanted knock on the door on Friday morning.
On resumption after the game was reduced to 46 overs per side, Ronchi struck four boundaries and a six to bring up his fifty off 33 deliveries.
This was Williamson's maiden century against Australia with his previous best being 81 which came in December 2016 at Canberra.
Guptill and Williamson will be the key to New Zealand, and also crucial to the side's fortunes will be the form of the experienced Ross Taylor, Corey Anderson and Luke Ronchi.
Placed in Group A alongside New Zealand, Bangladesh and England, the reigning World Cup champions face the hard task of adjusting fast to the demands of the 50-over version of the game and to the conditions in England as they try to win the Trophy for a record third time.
For New Zealand's captain, Kane Williamson, who top-scored on the day with a well-paced 100, the game was not completely wasted.
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After dismissing the Blackcaps thanks to some excellent bowling from Josh Hazlewood, who took 6-52, Australia lost David Warner (18), Aaron Finch (8) and Moises Henriques (18). Starc as usual bowled with pace and aggression as New Zealand were four without loss after the first over. "Let's hope it's rust and let's hope it's gone".
"He's (Mitchell Starc) a seasoned campaigner and now he's played a lot of cricket. Kane timed his innings beautifully, played really well throughout the middle but we did not bowl well at all".
The pursuit looked to be fatally undermined and Smith pulled no punches in his assessment, particularly in the efforts of a bowling attack rated as one of the tournament's most fierce. "We gave them a lot of freebies and it was pretty ordinary to be honest with you", he said.
Asked for his feelings when, with eight to his name the players left the field for the final time, Smith replied: "We still had some batters in the shed but I would have preferred to have been in New Zealand's position at the end".
The Australians will be playing One-Day Internationals (ODI) after a significant gap, having played four Test matches in India before taking part in the Indian Premier League (IPL) Twenty20 tournament. "Because that was pretty ordinary". The dismissal, however, didn't affect them as Williamson and Ronchi went about their batting without much fuss.
Competition for bowling places has led to some lively training sessions for Smith and his fellow batsmen and he hopes that will put them in good stead in the tournament proper.
After failing to win a game in their trophy defense in 2013, Australia intend to regain the championship by blasting all-comers.