All memories of their pre-season encounter were forgotten early in the match as Haven showed they were a much-changed side.
They took the game to their visitors and, despite being pegged back on a couple of occasions, they had enough in the tank to see it home.
There were good performances from Elliott Miller, who marked his 100th career appearance with a try, and Jordan Burns broke through on several occasions.
But across the board, Whitehaven lifted their game against their rivals for the title.
It was a nervy start from both teams with Newcastle making a number of unforced errors which handed Haven field position.
And after 12 minutes, they finally made it count. After pressurising the Thunder line, Forster managed to slip a pass across the line to the supporting Elliott Miller and he just had to touch down.
Paul Crook tagged on the extras and the home side had the early advantage.
A penalty for a high tackle saw Newcastle move down the field quickly and on their first real attacking threat on the Haven line, they scored.
Thunder whipped the ball out to the right-hand side and used the overlap for Ali Blair to cross in the corner, Benn Hardcastle adding the extras from the touchline.
But Haven were quick to hit back as they punished a dropped ball from Liam McAvoy inside his own half.
They came out to the right-hand side and Miller put out a great cut-out pass, and winger Jordan Burns collected and darted through three men to dive over the line. The kick into the wind was missed.
The referee then put an incident on report as Crook looked to kick on the last and the Newcastle defender charged it down, leaving Crook on the floor injured and having to leave the field.
Whitehaven kept getting ahead, only to allow Newcastle back into the game and the pattern repeated itself before the break.
With five minutes of the first half remaining, James Newton created the space and drew in the defence to allow Scott McAvoy to charge his way over the line, with Steve Roper’s attempted conversion hitting the post.
Then, a mistake from Glenn Riley saw the ball come loose near their own try line, and Haven gave away a penalty to let their opponents attack with purpose.
And they did just that as Lewis Young came running out to the left and then popped the ball up to prop Rhys Clarke who was supporting in the centre and he ploughed over.
Hardcastle landed a second touchline conversion as the half-time hooter sounded with Haven narrowly ahead 14-12.
It looked as though Haven had the perfect start to the second half when Riley charged over the line, only for the referee to disallow it for a forward pass.
But they got their reward shortly after as a grubber kick from Steve Roper went across behind the sticks and McAvoy pounced to score.
Newcastle were running hard with Daniel Parker looking set to score but the Whitehaven defence were closing in. He popped it out to Lewis Young but the half-back dropped it over the line.
Joe Brown handed Newcastle their opportunity to get back into the game as he intercepted a pass from Miller on his own 30-metre line.
He shot off the mark and then passed to the speedy Ali Brown who took off down the field with Miller trailing in his wake and touched down, with Hardcastle adding the extras.
Hardcastle then took his chances with a penalty just over 35 metres out from the posts and he powered it over to level the game at 20-20.
Newcastle were on a roll and Lewis Young took on the line again and broke through but an ankle tap from Miller slowed his progress.
Player/coach Carl Forster then lifted the home fans as he broke through on the halfway line and outpaced the visiting defence to touch down. Roper converted and Haven had the edge again.
Roper then looked to add two more vital points to the scoreline with a penalty 37 metres out and to the left of the posts, and he did just that to afford his side some breathing space.
Then came the try that sealed the victory. It all began with a great break from Jordan Burns, supported by Miller, which took Haven to the Newcastle try line.
Glenn Riley made certain as he burst over the line to make up for the one he had disallowed earlier in the game, and Roper added the conversion with ease.
Whitehaven finished the game with just 12 men as Marc Shackley was sent to the sin bin for a professional foul.
But they held out despite a couple of late flurries from Newcastle, who also finished with 12 men with Evan Simons being yellow carded for punching in the tackle.
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