The victory was Arbroath's best result in a couple of seasons but not enough to satisfy McGlashan.
He said: "We never really got into our stride.
"We put the game beyond Stranraer with two early goals then gave them a lifeline and switched off."
Robbie Ross sparked the goal glut in five minutes.
A Marc McCulloch corner was headed back into the middle by Robbie Raeside and Ross forced the ball over the line from close range.
Three minutes later Stranraer keeper Scott Black felled Ross in the box and was lucky to escape with just a yellow card.
Raeside finished clinically from the spot, firing the ball out of the reach of the diving Black.
Things could have been even worse for the Blues in 11 minutes when a David McGowan header looked to have crossed the line but referee Thomas Robertson awarded a goal kick. The visitors were in complete control and Ross almost added another but fired a shot wide.
Home striker Stephen McConalogue threw the Blues a 23rd-minute lifeline though with a goal from an acute angle.
Martin McBride swung a corner beyond the back post and McConalogue squeezed the ball home.
However, Arbroath regained control and McGowan's glancing header from Barry Sellars' free-kick in 37 minutes restored their two-goal lead.
Stranraer were reduced to 10 men just three minutes into the second half when McBride was shown a second yellow card.
Ross netted his second in 68 minutes, heading a Sellars cross wide of Black, then Kevin McMullan put the seal on victory in 77 minutes with a powerful shot.
Ref Robertson booked six Stranraer players and one Arbroath but Blues boss Keith Knox was more concerned with his side's dodgy backline.
He said: "Poor defending has again cost us dear and that's 17 goals we've conceded in four games."