Next up in Arthur Ashe Stadium, it's Wimbledon champion and No.3 seed Garbine Muguruza against the Czech Republic's Petra Kvitova (13). Muguruza is hoping to continue her bid for another Grand Slam title and strengthen her hopes of ending this tournament as the world No.1.

GAME, SET AND MATCH! - MUGURUZA 6-7 3-6 KVITOVA. It's a nervy finale, but Petra gets there in the end. At 30-0 she's cruising before a couple of double faults leave her in trouble. She fights hard to fend off three BPs before getting the job done in one hour and 46 minutes. She now faces a mouthwatering quarter final showdown with Venus Williams. Muguruza's dream of leaving the US as world No.1 is in the balance and she now needs results to go her way in the coming days.

MUGURUZA 6-7 3-5 KVITOVA. Power, depth and precision from Petra - but despite the big forehand doing all sorts of damage, Muga saves match point before keeping her slim hopes alive from deuce. Gutsy. Kvitova will now aim to serve it out...

MUGURUZA 6-7 2-5 KVITOVA. Muguruza takes the first point after coming out pumped up but can only watch in frustration as her majestic forehand to the corner is curved past her on the run by an even better one from Kvitova. The Czech shakes her fist to the crowd and then saunters through the next three points to move within a game of the last eight.

MUGURUZA 6-7 2-4 KVITOVA. Garbi wriggles off the hook as Petra twice blazes long at 15-30 before a backhand with real depth proves too awkward for the Czech to keep the rally alive.

MUGURUZA 6-7 1-4 KVITOVA. The No.13 seed consolidates to 30 with relative ease. It's gone from a quite exhilarating contest to a very one-sided affair in the past 10-15 minutes. Muguruza is leaking some very basic errors and it's likely to cost her a place in the last eight.

BREAK! - MUGURUZA 6-7 1-3 KVITOVA. Alarm bells blaring for Muguruza. She's on the ropes right now. A horrible backhand miscue gifts Kvitova another break.

MUGURUZA 6-7 1-2 KVITOVA. The momentum is firmly with Petra. She rampages to a love hold to claim the scoreboard advantage. Muguruza's forehand continues to be a clear weakness.

BREAK! - MUGURUZA 6-7 1-1 KVITOVA. Muguruza's air of superiority from the start of Set 1 is long gone. She's struggling at times, particularly on serve. She comes nowhere near consolidating as she is broken to love to allow Kvitova back in instantly.

BREAK! - MUGURUZA 6-7 1-0 KVITOVA. Magnificent response from Muguruza or a real lull from Kvitova? Probably a bit of both as the Spaniard shrugs off her tie break woes to instantly make a breakthrough on the final point of triple BP. Kvitova fought hard to stave off two but then hooked a backhand wide of the tramlines.

SET - MUGURUZA 6-7 KVITOVA. After a titanic battle lasting over an hour, it's Kvitova who comes through 7-3 in the tie break. The Czech crunches down an overhead to seal it after Muguruza's huge miss on a volley and a double fault proved to be the key moments in the breaker.

TB UPDATE: It's 3-3 at the change of ends. Muguruza led 2-0 and 3-2 but has been pegged back just like she was during the set.

BREAK! - MUGURUZA 6-6 KVITOVA. A real shocker from Kvitova. She double faults on the second of three break points and gives Muga the lifeline of a tie break.

BREAK! - MUGURUZA 5-6 KVITOVA. Petra is really enjoying this battle now. She finds a way back in from 30-0 down and targets the misfiring Muga forehand. It's a smart tactic that pays off - and then some. The Czech breaks when her opponent fires a desperate drive long and will now serve for the set.