Wagner picked up opener Alastair Cook's wicket with what he described as a wide half-tracker. Cook whacked it straight to Hamish Rutherford, though.
The next delivery was a beauty and definitely part of the plan. If you are going to get Kevin Pietersen's wicket, then your best chance is to strike early.
Wagner speared in a full delivery, which swung and trapped the classy right-hander in front, for a first-ball duck.
''Getting Kevin's wicket was massive during the warm-up game [in Queenstown last week] but getting it in a test is even better,'' Wagner said.
''If there is any wicket you want that was the one. I'm real pleased with that.
''Today was just one of those days when it did not really feel that great but things just happened. I bowled a wide half-tracker to Cook and he hit it straight to point. So it was just one of those days.''
Wagner had to work harder for his next two wickets, removing the in-form Ian Bell for 24 and James Anderson for 23.
While Wagner felt a bit lucky with his day, his team had deserved its success.
''I think on the day we just executed what we needed to do and it worked for us.
''If there was anything in the wicket which was going to help the bowlers, it was going to be in the morning. We had to make the most of it and we did.''
The irony is Wagner might not have played, had Doug Bracewell not been ruled out with a cut foot.
