Baxter got lucky with his first spot-kick, converting the rebound after missing, but didn't pass up when presented with a second opportunity after Charles handled in the area.
However, Latics boss Johnson admitted he doesn't think he will be able to take similar dramas should they arise often throughout the new season.
"That was real heart attack stuff wasn't it? It was incredible really but overall I felt we deserved to take the victory," said Johnson. 2I would much rather win 4-0 than 4-3 though.
"We have got a new side here but everyone can see we have got goals in us. I was disappointed with a couple of the goals we conceded.
"Though at the end of the day, we have come away with the three points from a really tough place. We have had a good summer and all the lads have gelled really well.
"We have been exciting in our friendly fixtures and I think the fans have taken to that. There is togetherness there and a spirit.
"It can be a bit scary when you are hanging on like that at the end, but I'm not complaining. All the players have worked so hard and they have got the rewards."
- Sports & Recreation
- Jose Baxter
- Darius Charles
- James Tarkowski
- Greg Tansey
- Filipe Morais
- Cristian Montano