Valkerie Baynes is a general editor at ESPNcricinfo
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Haynes, Meg Lanning's deputy, started slowly on a Hamilton pitch that proved tricky to score on early, before the pair broke the shackles in a 196-run second-wicket partnership as England's bowlers struggled to make inroads. Australian spinners Alanah King and Jess Jonassen shared five wickets between them to defend their total of 310 for 3 in a 12-run victory for the tournament favourites.
Before the match, Lanning had identified Haynes as vital to her side's title aspirations.
"She's a very important part of our squad on and off the field," Lanning said in her pre-match press conference. "For me personally, she's been incredible and really does make my job a lot easier.
"She comes in in good form. She's an important part of the team. She's going to play an important role for us if we are to win this World Cup and I can't really see her stopping anytime soon, to be honest. She's fit, she's strong, she's playing well, and she's playing important role for the team. We'll see what happens after this World Cup but I could see her playing for a long time down the track."
At 35, Haynes is the oldest member of the Australian squad and had taken three months off last year through a combination of a hamstring injury, interstate travel restrictions and parental leave to be with partner Leah for the birth of their son, Hugo.
She returned to international action during the Ashes series in January, scoring a half-century in the drawn Test - again combining with Lanning for a 169-run first-innings partnership, while her highest ODI score for the series was 31 in the third and final fixture in Melbourne.
But Haynes was in fine touch as she scored an ODI career-best 130 against England on Saturday, patiently riding out the first half of the innings with wicketkeeper Amy Jones standing up to the stumps almost from the outset as she reached 39 not out off 60 deliveries before she and Lanning began to make the most of having plenty of wickets in hand.
"It's funny, coming into this game I was probably a little light on runs," Haynes said. "I didn't feel out of nick but I was just getting out early, so it's really nice to make a contribution today. I think our top four is going to play a really big role in this tournament and our ability to go and score big hundreds is going to be really important, particularly on flatter wickets."
Haynes was almost lost to the sport in her late 20s after dropping out of international reckoning for more than three years. But she was recalled in early 2017 and made vice-captain a year later. Now she is one of Australia's most experienced players, having played 69 ODIs and 75 T20Is, including six World Cups across both formats.
"I think in tournament play it's good to have those tight contests and be pushed," she added. "England certainly did that today and to walk away with the win is obviously a really positive start to our campaign. Our goal is obviously to be a part of the business end and playing finals and those sorts of things. It's nice to get that first one away."