Sellars stunned the Sons with his monster strike in the 15th minute which flew over the head of keeper Michael White and into the net.
McGlashan beamed: "Barry's goal will take some beating this season. I don't think we'll see a better one.
"He has scored a few fantastic long-range goals and I think the wind carried this one a bit.
"It was a great win and I'm delighted with our display."
Sellars could have doubled his goal tally in 29 minutes but the midfielder blasted a low shot inches wide.
Steve Hislop made it 2-0 to the home team a minute after the break when he powered home a header from Mark McCulloch's corner.
Sons pulled a goal back when Roddy Hunter scrambled the ball home from close range after Ian Chisholm's long throw caused chaos in the box.
But Dumbarton's hopes of a comeback were dashed when sub Robbie Ross slotted home Sellars' low cross in the final minutes.
Dumbarton boss Jim Chapman said: "We played some nice football but were caught out in the final third and made some silly mistakes."