Though she had taken out No.22 seed Varvara Lepchenko in the previous round, Arruabarrena-Vecino's run seemed to be coming to a close as the No.14-seeded Vinci cruised through the opening set in just 27 minutes; but Arruabarrena-Vecino stayed even with her through 4-all in each of the next two sets and pulled away just enough each time, eventually emerging with a 26 64 64 victory.
Arruabarrena-Vecino was 0-4 against Top 20 players going into the match, all four losses in straight sets and barely winning any games either - she won a total of 11 games in four matches against Svetlana Kuznetsova, Agnieszka Radwanska, Ana Ivanovic and Angelique Kerber. That all changed.
The road only gets tougher, though - next up for Arruabarrena-Vecino is No.2 seed Maria Sharapova, who beat another Spaniard, No.25 seed Carla Suárez Navarro, 75 63. Suárez Navarro was up in both sets - 5-4 first set, 3-2 second set - but both times Sharapova shifted to another gear to close it out.
"I thought it was a tough one - she's a quality player, capable of playing some really good tennis," Sharapova said of the Spaniard. "She's dangerous. She's beaten top players in Grand Slams before and has a really solid game with a lot of variety, and she can hit the ball as well. She's really tough.
"There are a few things I want to improve on, but I was happy I got through on not a great day."
Sharapova talked about Suárez Navarro's classy one-handed backhand. "Players are able to open the court up a little more with the angles, and they use the slice a lot more when they're a one-hander," she said. "I think it's about having someone hit you a few more slices than usual in practice, because most one-handers usually have a pretty good slice. And against me those players do like to use that."
Sharapova and Arruabarrena-Vecino will be playing against each other for the first time.
"I don't know too much about her - I hope my coach was out there watching the end of that one," Sharapova said about her next opponent. "She's played a lot of matches, and I've kind of played a bit of a similar style to her in this tournament so far, but I'm sure I will find a couple of videos to look at and to get a good look at her myself. Sometimes you don't always believe what the coach says!"
For the 20-year-old Arruabarrena-Vecino, this will be one of her biggest matches - Sharapova was asked about her first big match on a big stadium, and that actually came right here at Indian Wells.
"This was the first big stadium I was on," Sharapova said. "Indian Wells was the first big professional event I was a part of. I think it was Samantha Reeves who I played against in the first round, and I think I beat her, and that set up the match to play Monica. It was a big deal because I was 15 or so.
"You don't know what to expect. I think actually the first round I did play on center court against Samantha, and I was able to win that one - and I certainly had no chance at all in the next one."