Himmelberg took a soaring mark and kicked what turned out to be the match-winning goal in Sunday afternoon's 10.17 (77) to 11.9 (75) thriller.
He then went to the other end of the ground and with about a minute left, Hawthorn's Jarman Impey launched a booming shot from more than 50m out.
Himmelberg was on the goal line and after a score review, it was ruled he touched the ball before it went over the line.
Norwood Oval was again a Gather Round success, with a full house of 9057 for the pulsating clash.
As the scores suggest, the Giants went close to ruing their appalling inaccuracy.
Himmelberg's fellow key forward Jess Hogan also took a big mark 25 minutes into the last term, but missed from 20m, directly in front.
Giants midfielder Tom Green was best afield with 31 disposals and nine clearances, but he is in match review trouble after his tackle in the second term that slung Josh Ward to the ground.
Hawthorn's Will Day is serving a two-game ban and Geelong forward Gary Rohan missed this weekend because of falling foul of match review with similar tackles.
Essendon captain Zach Merrett was also banned for one match on Sunday for his tackle in Saturday's win over Melbourne.
Given Hawthorn's barren third quarters so far this season, the signs were bad for them at the main break.
In their previous four games, the Hawks had only managed one goal in the third quarter.
The Hawks had kicked the first two goals in the opening four minutes of the game, but GWS stifled their quick start and slowly took control.
Despite having double the inside 50s early, Hawthorn did not add to their goals for the rest of the term and only led by a point at quarter-time.
No.1 draft pick Aaron Cadman was mobbed by Giants teammates when he kicked his first AFL goal on debut late in the quarter.
Inevitably, GWS took the lead in the second term and broke that out to 15 points early in the second half.
But as the Giants struggled to convert, Hawthorn kicked the next four goals to lead by eight points at three-quarter time.
Hawks captain James Sicily was awarded a 50m penalty that put him at point-blank range at the Roger Woodcock end and he celebrated by booting the ball out of the ground.
Giants captain Toby Greene kicked three goals, while Fergus Greene put through three for the Hawks.
Midfielder Jai Newcomber relished the tight dimensions of Norwood Oval and starred for the Hawks.
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