Here are four things to watch for on day nine of the US Open on Tuesday.

1 Petra Kvitova, who missed part of the 2017 season after a home invasion left her with a badly cut left hand, continues her remarkable comeback when she faces American Venus Williams.

2 American Sloane Stephens, who recently returned to the ATP tour following an almost year-long absence due to a foot injury, will battle 16th-seeded Anastasija Sevastova of Latvia.

3 Spaniard Pablo Carreno Busta, fresh off his fourth round win over 18-year-old Canadian Denis Shapovalov, will take on 29th-seeded Diego Schwarztman of Argentina to kick off the action at Arthur Ashe Stadium.

4 Sam Querrey, the last American man standing, faces off against big-serving Kevin Anderson of South Africa under the lights on Arthur Ashe.