It was end-to-end hockey in the second half before Herewini produced two top-class finishes in the 44th and 58th minutes to secure Midlands' first Ford NHL crown since 2008.
Canterbury midfielder David Brydon was named Men's Most Valuable Player for the tournament while Central striker Martin Atkinson scooped top goal scorer with 10 field goals from seven games.
In the women's K Cup final, the Canterbury Cats held on to defeat North Harbour 3-2.
Canterbury came out firing and opened the scoring in the 11th minute when Olivia Merry went on a solo run and fired an amazing shot into the net past the shoulder of goalkeeper Brooke Roberts.
The Cats doubled their lead 10 minutes later when Joie Leigh capitalised on a bobbling ball from a penalty corner deflection and knocked into goal.
North Harbour struck back through Stephanie Elliot from a 27th minute penalty corner before Canterbury netted again right on halftime from the stick of Jenny Storey.
Harbour lifted the intensity after the break and cut Canterbury's lead to one goal after Stephanie Dickins struck from a 46th minute penalty corner deflection.
Canterbury's steeled themselves on defence in the final quarter and kept North Harbour from scoring an equalising goal despite huge pressure.
Canterbury captain Jenny Storey took honours as Women's Most Valuable Player and Midlands striker Amy Robinson (Tauranga) finished top goal scorer, having netted five times during the tournament.
The Central Mavericks grabbed the men's bronze medal after a thrilling 3-2 shoot-out win against North Harbour, after the score was tied 3-3 at fulltime.
In the women's bronze medal match, Midlands put together a hard fought 2-1 result over Auckland.
Auckland opened the scoring for in the ninth minute when Deanna Ritchie got a great final touch on a crash ball into the circle from Samantha Harrison.
Midlands pulled level four minutes later thanks to a quick reaction from Lauren Turner who collected a loose ball and hit home on her reverse stick.
With the score locked up at 1-1 for much of the remaining game, Ellie McCleery delivered the winning blow from a goal mouth tussle five minutes from fulltime.