Elina Svitolina said she "was on a mission" for Ukraine after earning a straight-sets win over Russian opponent Anastasia Potapova in the opening round of the Monterrey Open.

The top seed donned the yellow and blue colours of her homeland for Tuesday's match and eased to a 6-2 6-1 victory in a little over an hour in Mexico.

Svitolina only agreed to play her opener after tennis authorities announced a ban on Russian and Belarussian players competing under the name and flags of their countries.

And as Russia's invasion of Ukraine entered its sixth day, the 27-year-old produced an impressive performance that saw her win 73.5 per cent of her first-serve points.

Former world number three Svitolina, who will now face Bulgarian qualifier Viktoriya Tomova, had previously announced she will donate her prize money to the Ukrainian army.

"It's a special one because of what we are going through right now in Ukraine, it's terrifying," Svitolina told reporters. 

"It's been six days and all the Ukrainian tennis players and Ukrainians who are there, we have been really terrified with what is happening.

"For me, playing the match here, I'm not playing only for myself. I'm playing for my country, I'm playing for the help of the Ukrainian army and people in need. 

"I was focused. I was on a mission for my country. From the beginning, it was important to be ready for anything that comes my way."

Petra Martic is also through to round two after recovering from behind to beat third seed Madison Keys 4-6 7-6 (7-3) 6-3.

Marie Bouzkova awaits following the world number 81's 4-6 6-2 6-4 win against Sara Errani. Number eight seed Ann Li's participation in the tournament came to an end with a 6-2 6-1 loss to Wang Xinyu, who will now face Brazil's Beatriz Haddad Maia.

Top seed Karolina Pliskova suffered a shock defeat while defending champion Bianca Andreescu and Coco Gauff also were on the wrong end of upsets Monday at the Indian Wells Open. 

World number 115 Beatriz Haddad Maia of Brazil stunned Pliskova in straight sets to reach the round of 16 at a WTA Premier 1000 event for the first time.

The 15th and 16th seeds, Gauff and Andreescu, also exited in two sets, albeit to seeded players. 

LUCKY LOSER OUSTS PLISKOVA 

Haddad Maia lost in the final round of qualifying but made the main draw as a lucky loser when Nadia Podoroska withdrew through injury, and she has made the most of that reprieve with a 6-3 7-5 defeat of the world number three. 

She had faced Pliskova once before and it did not go well, a 6-1 6-1 rout at the 2018 Australian Open, but the Czech struggled to find her trademark serve amid powerful winds in the California desert.

Pliskova suffered 12 double faults and won just 43.4 per cent of points on her serve, whole Haddad Maia saved nine of the 14 break points she faced on her own serve. 

KONTAVEIT STAYS HOT TO DETHRONE ANDREESCU

Haddad Maia next faces 18th seed Annett Kontaveit, who ousted Andreescu 7-6 (7-5) 6-3 to end the Canadian's dreams of a repeat. 

Kontaveit has won 15 of her last 16 matches, winning titles in Cleveland and Ostrava during that stretch. Monday, she captured the first set on her fifth set point before rallying from a 3-1 deficit in the second to run the table and seal the win.

"It was extremely close throughout the match and I was just trying to stay tough. I was ready for a tough match," Kontaveit said. "She's such a good player, such a great competitor, so I knew it wasn't going to be over until it was really over."

BADOSA BOUNCES GAUFF

Paula Badosa, the 21st seed, breezed past Gauff 6-2 6-2 as the American teen also had trouble with her serve, hitting just two aces after recording 12 in her previous match. 

In a meeting of the last two defeated finalists in the tournament, 10th seed Angelique Kerber beat 20th seed Daria Kasatkina 6-2 1-6 6-4. 

Third seed Barbora Krejcikova handled Amanda Anisimova with ease, 6-2 6-3. 

Ons Jabeur, the 12th seed, had little trouble in downing 22nd seed Danielle Collins 6-1 6-3.