Twelve months ago, a run through qualifying and into the last eight in Rio sparked an impressive upturn in form for Begu, who would end the campaign perched back inside the Top 50. On her return to the Jockey Club Brasileiro, the Romanian is seeded No.2 and looked every inch the title challenger in dispatching World No.214 Mattek-Sands, 6-2, 6-4.
The only previous meeting between the pair came a little over two years ago in Linz. On that occasion Begu came out on top over three topsy turvy sets and, despite her American opponent's lowly current ranking, she went into the rematch expecting another difficult outing.
"It was a really tough match because Bethanie's a great player, even if she's now quite low in the rankings," Begu said. "I knew from the beginning that I'd have to fight for every ball and in the end I won - so I'm happy!
"We played once before and it was a close match. She's been high in the rankings before and if my level dropped she is very dangerous."
Next, Begu will face Julia Glushko, who reached her first WTA quarterfinal by knocking out Grace Min, 6-3, 6-1. There was also disappointment for the third and final member of the American contingent in Rio, as No.4 seed Madison Brengle slipped to a 7-5, 0-6, 7-5 defeat against Dinah Pfizenmaier.
Meeting Pfizenmaier in the last eight will be No.5 seed Johanna Larsson after she overcame a partisan crowd and some tricky moments to see off Brazilian wildcard Gabriela Ce, 7-6(4) 6-4. "It was a true battle. The crowd was so noisy and she was fighting until the end. I had to play my best to win and I'm pleased with how I played at the important moments," Larsson said.