Jamie Mackie's second-half strike proved the vital moment in the game, but Argyle spent much of the proceedings on the back foot and were fortunate to see Adam Johnson miss a penalty.
"I am delighted with the win and delighted with the work-rate," he said. "We had some nervous moments - the penalty was one and (Kari) Arnason cleared one off the line - but you are not going to come to Middlesbrough and not get that.
"But we didn't just sit back. We had our chances too and their keeper had to make a few good saves too.
"We worked hard at the back and in midfield to keep a quality side at bay and we scored a great goal.
"Jamie Mackie caused mayhem for them. Their centre-backs won't have a harder afternoon all year. It was a good goal, a good touch to take him through and a good finish."