Italian 19-year-old Sinner is a fast-rising new star of the men's game and now has a ranking to match his age. However, he was put in his place by Novak Djokovic last week in Monte Carlo, before the world number one was himself dealt a jolting defeat by Dan Evans.
Sinner sped past Belarusian Egor Gerasimov in the first round in Barcelona on Tuesday, winning 6-3 6-2, and it will be wily world number 11 Bautista Agut who stands in his way of going deeper into the tournament.
In two meetings on hard courts this season, Sinner has edged out 33-year-old Spaniard Bautista Agut in tight deciding sets, and now they face a reunion on clay.
"He lost in Dubai against me, he lost in Miami against me, now we play once more here, so it's quite a small period of time," said Sinner.
"We're playing now our third match already, so it's going to be a very tough match. He is very, very solid. I never played against him on clay. I'm trying to be ready in the best possible way."
Bautista Agut barged past fellow Spanish player Pablo Andujar, scoring a 6-4 6-0 win.
Sinner was proud to enter the ATP top 20 this week but sees it as just a step on his journey, saying: "Obviously it's a good number, but for me at the moment not that important."
He added, quoted on the ATP website: "[I'm] just trying to improve day after day with my team and trying to improve as a player and the ranking is what it is. I'm happy to be top 20 player but the road is long so a lot of work to do."
Albert Ramos-Vinolas, Lorenzo Musetti and Frances Tiafoe, who fought off 17-year-old Spanish prospect Carlos Alcaraz, were also among Tuesday's winners in Barcelona.
Star turn Djokovic begins his campaign at the Serbia Open on Wednesday when he tackles Kwon Soon-woo, with the 18-time grand slam winner having received a first-round bye.
Tuesday's play in Belgrade saw wins for, among others, Federico Delbonis, Aljaz Bedene and Miomir Kecmanovic.