Robertson, 33, gave up three hits and struck out three while throwing 31 pitches.
"He was good," manager Eric Wedge said. "I liked the way he used his fastball on both sides of the plate. He was getting underneath some bats with some breaking balls. He was strong today."
Robertson knows he needs to make an early impression, given he signed a Minor League deal and will need to force his way onto the 40-man roster to get a job out of camp.
"At any given moment, it's game on," he said. "I think early on they just look at guys getting into the routine of things, but it's coming quick [to] where it's evaluation time. They're not handing out Cy Young Awards in Spring Training, but at the same time, people have to make this team. There are jobs to be filled, and they'll have to make decisions.
"They're not going to be fun decisions, but you just want everybody in here to have a healthy competition, stay healthy and have fun. There's nobody that's not pulling for the next guy. Everybody needs to put their best foot forward, and obviously pretty quick."