The 21-year-old played just 18 minutes after Gary Cahill's dismissal saw him subbed off for tactical reasons.
But Boga remains proud of achieving his goal of playing for the first-team.
"Yes, it was very surprising for everyone including me to start that game," Boga told Goal.
"In pre-season, I went with the first team and for me it was just to add numbers. But I said to myself, 'I will train hard and you never know, I might get that opportunity.'
"In the Arsenal game [in China] that is what happened because [Pedro] got injured. It was unlucky for him, but it was an opportunity for me. I went in and after that I got more game time. Then when we came back to England I was training well, because I knew there was a player out with a red card so it was an opportunity to take.
"Luckily, I got my 15 minutes. I think on the day and the day after, I was really sad. I think that is a normal feeling because, for me, I was waiting for that chance for a long time. After that, I got back up and trained as hard again because I couldn't keep staying down about it. You have to make sure when the next opportunity comes that you are ready.
"Everyone knows how hard it is to play for Chelsea, so for me, whether it was just one minute or two minutes, I don't care. It was really a proud moment for me and my family. I now look back on it with pride, yes."