Under the No.1 Court roof, No.2 seed Aryna Sabalenka kicked off the first Wimbledon in two years with a 6-1, 6-4 rout of qualifier Monica Niculescu in 1 hour and 15 minutes.

"Of course in the beginning, I was really nervous to open Wimbledon and also be first playing on [No.1] court," Sabalenka said, in her post-match press conference. "But, really happy that I won that match. The atmosphere there was unbelievable. I was enjoying it. People were supporting really well."

The result was only Sabalenka's second main-draw win at The Championships, and first since defeating Irina Khromacheva on her 2017 debut. On her last visit in 2019, the Belarusian crashed out in the first round to the wily grass-court expert Magdalena Rybarikova.

But Monday, installed at her highest seeding in a Grand Slam, there were little signs that Sabalenka would be undone by one of the most unorthodox players of the past decade. The 23-year-old used Niculescu's softer shots as target practice and was a whirlwind of power as she slammed 47 winners to 30 unforced errors.

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The Romanian's serve, which averaged just 129 km/h, was particularly vulnerable. Sabalenka clouted 15 clean return winners off it, and the third game of the second set saw Niculescu essay a desperate underarm delivery. It went into the net, and the World No.191 merely shrugged.

Niculescu, 33, had last beaten a Top 10 player in 2017 (Johanna Konta in Beijing), and had lost her first eight matches of 2021. But the grass swing has seen her turn around her season with six victories, including qualifying without dropping a set. 

The former World No.28 pulled off intermittent moments of magic that delighted the crowd. Her best points were finished delicately at net, where she found six of her eight winners of the day. After battling through a four-deuce game to break Sabalenka for the first time in the fourth game of set two, Niculescu was able to make the passage of play rather more competitive.

But despite Sabalenka's errors mounting in the face of improved Niculescu defence, the two-time 2021 titlist was ultimately able to balance both power and accuracy to keep in front. Niculescu would hold after three deuces to force Sabalenka to serve out the win - which she did with panache, even pulling off a serve-and-volley to reach match point.

Indeed, perhaps the greatest positive for Sabalenka was not only her ability to hit through Niculescu's spins and defence, but her success at out-duelling her opponent in several cat-and-mouse plays. Sabalenka frequently came out on top of dropshot exchanges, pulled off a winning shot off one of Niculescu' best lobs, and was proficient on the slice herself.

"Monica was playing a little bit better," Sabalenka said, regarding the close second set. "My legs were getting heavier, so I wasn't adjusting the ball that well, like I was doing in the beginning of the match. It was just about her game and my movement. As soon as I fixed it, I was able to win this match. Really happy that I could kind of find this movement and my game back."

Next up for Sabalenka, as she seeks to make the third round at SW19 for the first time, will be wildcard Katie Boulter. Great Britain's Boulter defeated American qualifier Danielle Lao, 6-7(6), 6-3, 6-4 in two-and-a-half hours.

Swiatek power blunts Hsieh tricks

Also successfully navigating an unorthodox opponent on No.1 Court was No.7 seed Iga Swiatek, who got past Hsieh Su-Wei 6-4, 6-4 in one hour and 15 minutes. 

The 20-year-old was the Wimbledon junior champion in 2018, but lost in the first round of her only previous senior appearance in 2019 to Viktorija Golubic. Last week in Eastbourne, where Swiatek lost in the second round to Daria Kasatkina, she said that "grass is not the surface I understand completely".

Given that context, the experienced Hsieh - who upset Simona Halep to reach the fourth round at SW19 in 2018 - could have been a potential banana skin. But Swiatek's understanding of grass is on a steep upwards curve, and against Hsieh she was anchored by a formidable serving performance.

The 2020 Roland Garros champion landed 65% of her first serves, won 79% of those points, and only faced two break points. Off the ground, she was quick to assert her authority with power. Indeed, such was Swiatek's pace that it was Hsieh who was unable to play her own game effectively and who ended up going for too much, committing 22 unforced errors to 16 winners - including six double faults.

"Su-Wei has great touch, and my main goal was to not let her use that," said Swiatek with satisfaction afterwards. The Pole also described her "great memories" of No.1 Court, the site of her junior final victory over Leonie Kung three years previously.

Osorio Serrano fights back again in thriller

One of the most thrilling atmospheres of the first day could be found in a battle of qualifiers on Court No.9, as Maria Camila Osorio Serrano pulled off yet another comeback 1-6, 6-0, 6-4 over Anna Kalinskaya in one hour and 30 minutes. It was the Colombian's first Grand Slam main draw win of her career, and she was cheered on vociferously by fans waving her country's flag.

"I’m so happy, I just don’t know what to say," Osorio Serrano told the media, after her win. "I really wanted to win this match, so many emotions.

"The first set, 6-1 for her, she was playing unreal. I didn’t know how I was going to turn the match in the second set, [but] I played very well, I was very strong here. That’s important, the mentality."

Osorio Serrano has now won 12 of her 13 deciding sets in 2021, and demonstrated her knack for finding her finest tennis with her back to the wall again. Serving down 3-4, 0-40 in the third set, having let a break lead slip, the 19-year-old found big forehands, superb defensive plays and exquisitely accurate lobs to will herself to victory.

"Third set, 4-3, 0-40, she had three break points, and I turned that game," Osorio Serrano said. "It was really important, because it could be 6-3 for her also."

Maria Camila Osorio Serrano's three-set matches in 2021
Q1 Australian Open, d. Barbara Haas 6-3, 3-6, 7-5
QF Boca Raton ITF W25, l. Claire Liu 6-7(2), 6-1, 6-2
Q1 Monterrey, d. Wang Xiyu 7-6(4), 4-6, 6-2
F Bogota, d. Tamara Zidansek 5-7, 6-3, 6-4
R1 Charleston 250, d. Magda Linette 6-3, 4-6, 7-5
R2 Charleston 250, d. Christina McHale 2-6, 7-6(2), 7-6(1)
Q1 Belgrade, d. Dalma Galfi 6-3, 6-7(7), 6-4
R1 Belgrade, d. Zhang Shuai 6-2, 1-6, 7-6(4)
Q1 Wimbledon, d. Liang En-Shuo 6-4, 3-6, 6-4
Q2 Wimbledon, d. Panna Udvardy 6-4, 3-6, 6-2
Q3 Wimbledon, d. Nuria Parrizas Diaz 3-6, 6-3, 6-2
R1 Wimbledon, d. Anna Kalinskaya 1-6, 6-0, 6-4