Robin was part of Alves' team, and it was known that Robin was Alves' best friend. The reason why he was willing to go first was to help out Alves. Everyone who attended this sparring match already knew that the five knights were of the God Rank. They could tell it by a single glance, but they still did it to test them out. They wanted to find out how strong these new people were.
Unfortunate for Robin, as he found it the worst way, he experienced the wide gap between him and the knight. The first one was a surprise, and as Jovrick said, Robin did not use his full power in his first strike, not with the second one.
