The 19 year-old opened the scoring with a wonderful solo effort after just ten minutes before later setting up Gabriel Jesus' goal just after half-time that made it 3-1.
Speaking after the game, Flick said:
"Look at the goal he scored, it's incredible. For me, he is the best player in the world and I love watching him play."
Flick guided his side to an eleventh win in as many games in all competitions to start their season and they picked off an in-form Betis side who have already seen off Real Madrid at their temporary home this season, with relative ease. There was also a first Barca goal for Rodri as well as strikes from Eric Garcia and Dani Olmo to round off a brilliant evening in Seville for the reigning LaLiga champions who are looking unstoppable so far this season.
Yamal was later booked and replaced on 70 minutes with the score at 4-2 but Flick insists it was nothing more than load management:
"Given the score we had to change him but I told him I was proud of his performance. He is under a lot of pressure but is 100% focussed and committed. That is how great players are made."
The Blaugrana head into a massive week with a titanic Champions League tussle with Paris Saint-Germain on Tuesday before the first El Clásico of the season next Sunday. It will surely be a test of their mettle, but they have shown nothing so far to suggest they cannot rise to the occasion.