But the final 10 overs produced a remarkable 139 runs as things unravelled quickly in the field for Bangladesh after their great start. Williamson was dropped twice and captain Mortaza had to leave the field after injuring his hand trying to stop an Anderson thunderbolt.
Bangladesh began needing 9.78 runs per over with Tamim Iqbal and Soumya Sarkar looking good on the excellent batting wicket. They raced to 44 before Tauranga's Trent Boult broke the partnership, removing the dangerous Iqbal.
Sarkar kept blazing away to get his team to 75-1 off seven overs before Ish Sodhi took a great running catch off his own bowling to end his promising knock at 42.
But he needed to kick on to a big score which has typified the Bangladesh batting on tour.
Williamson enticed Sabbir Rahman into an ugly slog and with seven overs left Bangladesh needed nearly 13 per over. Experienced pair of Mahmudullah and Shakib Al Hasan were their last hope. They took 14 off Boult to leave 75 off six overs, before Sodhi removed the dangerous Mahmudullah.
And that was the end of the Bangladesh resistance.
Anderson said it was special to make such a telling contribution.
"I have been in the wilderness for a little bit from international cricket so I guess it was nice after two low scores to come back in and get that score and have a decent total on the board," he said.
"I wasn't part of the one-dayers but the Twenty20 has been a pretty clinical performance and a pretty clinical series victory. They will take a lot of confidence going into the tests with that high of what we have done over the last few days."
The big-hitting left hander was not getting too carried away after his innings but said it was reassuring.
"You always have times when you have form slumps and you go through periods when you are not getting runs and you start questioning yourself.
"When you do something like this you can relax a bit and try and feed off it and get a bit of rhythm into other games as well."
The smiles on the spectators' faces leaving the ground were matched by NZ Cricket officials, with 14,000 packing in over the two games an outstanding return.