Moscow - Ukraine's Sergiy Stakhovsky has produced the biggest upset on Monday on the first day of the ATP and WTA Kremlin Cup, ousting Portuguese seventh seed Joao Sousa in straight sets.
The 27-year-old Ukrainian -- who gained his biggest ever scalp at Wimbledon this year when he beat Roger Federer for his first ever win over a player ranked in the top 10 -- beat 24-year-old Sousa 6-4, 6-3 in one hour 17 minutes.
Sousa, ranked 50th in the world in comparison to his opponent's 98th, started the tie confidently, taking a 4-1 lead with a break in the fourth game.
However Stakhovsky, who won the last of his four ATP titles in 2010, was unfazed and stormed back to break Sousa twice and rattle off five consecutive games to win the first set in 37 minutes.
In the second Stakhovsky underlined his supremacy when he broke Sousa, who in September became the first player from Portugal to win an ATP title when he won the Malaysian Open, twice again in the second set to clinch the match.
"I was a bit nervous to start with and experienced problems at the beginning," Stakhovsky said.
"But later in the first set I managed to regain ny concentration and dominated the rest of the match."
In the next round he will face French journeyman Edouard Roger-Vasselin who beat Czech rival Jiri Vesely 6-3, 6-7 (3/7), 6-3.
The 29-year-old Roger-Vasselin looked more focused from the start breaking his rival's serve twice to take the first set in 32 minutes.
They traded breaks throughout the second set as it went to a tie-break which 20-year-old Vesely won to tie the match.
Roger-Vasselin came up with the decisive break in the eighth game of the third set and won the match in 2 hours 16 minutes.
The women's tournament saw France's 26th world ranked Alize Cornet, who is seeking her fourth title, beat Ukraine's Elina Svitolina 7-5, 6-3 in one hour 42 minutes.
Cornet booked a date with either seventh seed Samantha Stosur of Australia or Estonia's Kaia Kanepi in the clash for a place in the quarter-finals.
Local favourite and two-time Grand Slam title winner Svetlana Kuznetsova, seeded eighth, advanced into the second round on the back of a 7-5, 6-2 victory over another Ukrainian Lesia Tsurenko.
Results from the first day of the ATP/WTA Kremlin Cup on Monday (x denotes seeding):
Sergiy Stakhovsky (UKR) bt Joao Sousa (POR x7) 6-4, 6-3
Karen Khachanov (RUS) bt Albert Ramos (ESP) 6-2, 3-6, 6-4
Horacio Zeballos (ARG x6) bt Ricardas Berankis (LTU) 1-6, 6-3, 6-4
Edouard Roger-Vasselin (FRA) bt Jir Vesel (CZE) 6-3, 6-7 (3/7), 6-3
Alisa Kleybanova (RUS) bt Varvara Lepchenko (USA) 6-7 (6/8), 6-4, 6-4
Alize Cornet (FRA) bt Elina Svitolina (UKR) 7-5, 6-3
Svetlana Kuznetsova (RUS x8) bt Lesya Tsurenko (UKR) 7-5, 6-2
Anastasia Pavlyuchenkova (RUS) bt Caroline Garcia (FRA) 6-0, 6-3