He then took the lead after the pitstops, and held off Mostert to win by 1.3 seconds.
"It's an awkward one," McLaughlin said of the clash, which had fans calling for him to be penalised for cutting part of the course.
"I didn't know if Fabian was 100 per cent there, I thought it was my corner, I was in front far enough.
"I went off the road and tried to get back and rejoin in the right position, but I was going to go the wrong way, so I was dammed if I did and dammed if I didn't.
"I pushed on and thankfully it was OK."
Coulthard cut an angry figure during the race after being penalised, but was more diplomatic after the race.
"You never want to hit your teammate – it's as simple as that. I'll apologise and put my hand up – obviously I got penalised for it.
"I think when you replay moments over and over again, you can get a better analysis of what's gone on, but we operate with tenths of seconds, and you make a particular decision at that time. If you can hit rewind you would.
"Our policy is to not hit each other, and unfortunately today I broke the policy."
David Reynolds, who incurred a penalty of his own on lap two after bumping James Courtney, rounded out the podium in third, with Courtney finishing fourth.
Mostert was content with his fifth podium of the season, despite having started from pole position, and had mixed feelings about McLaughlin's manoeuvre.
"I'll cry about it just to try and get first, but at the end of the day he got hit off, so it wasn't his fault that he went off.
"It's the toughest thing here, and with the rain it's very slippery, so it's hard to get back [to the track], but at the end of the day he was the fastest guy so I feel like he deserved the win."