Zagar won the final race of the night to extend the Robins winning margin
Swindon have finished top of the Elite League table at the end of the regular season, after beating Wolverhampton 51-39 at the Abbey Stadium on Thursday.
Leigh Adams led the way for the Robins with paid 14, while Matej Zagar and Morten Risager both scored 11.
Swindon boss Alun Rossiter told BBC Wiltshire finishing top is great, but there is more work to do.
"It's fantastic, absolutely wonderful; but it all starts again now building for the play-offs," he said.
Swindon now get their choice of opponents in the play-off semi final, which is almost certain to be Coventry, once the Bees secure their place in the top four.
The Robins will take an eight-point advantage into that tie, by virtue of their first-placed finish.
Zagar says the win was nothing less than they deserved for their hard work throughout the summer.
"We've proved that we've done the best job throughout the season, so I hope we get what we deserve in the end."
And the Slovenian star warned the other play-off teams that there is more to come from Swindon over the next month.
"I was not really at my top form today, and we had a few guys struggling, so I think we can do even better than this," Zagar said.
Swindon - Leigh Adams 13+1, Ryan Fisher 2+1, Simon Stead 8+1, Travis McGowan 4+4, Matej Zagar 11, Paul Hurry 2+1, Morten Risager 11
Wolverhampton - Fredrik Lindgren 11, Nicolai Klindt 5, Adam Skornicki 3+1, Tai Woffinden 11, Peter Karlsson 8, Chris Kerr 0, Lee Complin 1