First half goals by Sam Burnett and Mitch Megginson – the former Aberdeen man’s 49th of the season – were added to by Aiden McIlduff’s own goal and Jamie Masson’s superb late strike to give the Balmoral Stadium side what in any other week would appear an unassailable lead.
Mathieson said: “It is only half-time for us, if you look at the football over the past week when Liverpool and Tottenham both showed big scores can be overturned.
“It doesn’t matter if it’s Europe or this level, if you don’t go out and do the basics, and do your job properly, that’s what happens.”
Of top scorer Megginson, who went off with a groin strain in the second half, Mathieson added: “We took him off as soon as he felt a slight twinge. He’s been in and had treatment, we’ll rest him and do some yoga on Monday to loosen the players up so we hope he’ll be OK.”
The home side looked the more threatening from the off, and they went ahead midway through the first half when Ryan Strachan’s cutback was forced towards goal by Megginson and saved by Ryan Goodfellow in the Berwick goal. Jordan Orru’s attempt to clear then ricocheted in off Burnett to open the scoring.
It was 2-0 six minutes from the break when Darryn Kelly crossed for Megginson to head home at the back post.
The third came in scrappy fashion as substitute Jordan MacRae saw his header from a Masson cross saved, and as players from both sides went for the loose ball, McIlduff put through his own net.
Masson rounded off the scoring with a right-footed effort after 83 minutes.
Berwick boss John Brownlie says his side will change their approach for the return leg, noting: “We’re still in the tie, but we have to do a lot better than we did today. Cove will be very confident as they were far better than us today.
“We’re going to change our strategy for next week – we need to get an early goal and a bit of luck as Cove are decent. We’re fighting for survival and if the players realise that we have a chance. It’s hurting, which is a good sign.”