When a lower-ranked minnow is on a streak – the top players all say – you just have to hang in and hope they come out of it: lose form, lose their nerve. But some days they don’t. On paper, Ana Ivanovic’s meeting with Bethanie Mattek-Sands looked like one of the mismatches of the day. But Mattek-Sands – the world No158, best known for extreme outfits that have seen her compared to Lady Gaga – was just spectacular and dumped out the seventh seed in straight sets, 6-3, 6-4, with a relentless display of flamboyant, attacking tennis.

Mattek-Sands was an authentic underdog coming into this second-round match: only once in 2015 had the 30-year-old American won two singles matches back-to-back before now. She missed half of last year with a hip injury, her ranking dipping to 175, and entered the draw at Wimbledon only through the qualifiers. Ivanovic, meanwhile, is a serious contender on grass: a semi-finalist in 2007 and a reliable presence in the second week of the tournament. She had a run to the semi-finals at Roland Garros in June and appeared to be back to the form that made her world No1 in 2008.

From the start, though, the rankings looked skew-whiff. Mattek-Sands, wearing eye-catching long socks and a mesh-backed top, served and volleyed every chance she got, and her net skills were unerring. She moved into a 3-0 lead in a blink. Her singles performances might have been erratic this year, but she is the form doubles-player in the world now. With Lucie Saforova, Mattek-Sands has won the titles at both the 2015 Australian Open and Roland Garros – they are halfway to a calendar-year grand slam; she also won the mixed doubles in Paris with Mike Bryan.

It is not hard to see why Mattek-Sands has been so successful this year: her serve booms and she follows it up with boisterous, uncompromising groundstrokes. In just over an hour against Ivanovic, she hit 32 winners and just 18 unforced errors. The Serb, rendered tentative, could only reply with 15 of each.

For Mattek-Sands, however, the biggest change in her game in 2015 has been a mental one. “Being out for six months, having hip surgery, gave me a perspective on playing,” she said. “Last year I was watching these matches at home on television.” Even the improbable heatwave helped her against Ivanovic, she thought. “I feel like we’re in Florida – how hot is it out there.”

Only Wimbledon’s all-white dress code is cramping Mattek-Sands’ style a little bit. When asked what she would prefer to wear, she replied: “Well, I didn’t even wear white in my wedding, so not white. I mean, you can’t even wear off-white or cream. I was like: ‘Man, if you wash your whites too many times, they will be illegal.’ Better be washing it in cold water.”

The mood at Ivanovic’s press conference was less jocular. “I think I played a little too passive at the beginning,” she reflected. “She got off to a good start which give her confidence and I think that’s what made the difference in the end.”

Ivanovic eventually ran out of ideas and took to making imploring, beseeching glances to her team in the stands. In the front row was her boyfriend, the Bayern Munich midfielder Bastian Schweinsteiger, who appeared to be doing the tennis equivalent of kicking every ball. He leant forward on the railings, nervously gunning a bottle of water, he put his cap on, took it off. Tennis can be a tense business.

Mattek-Sands even showed a little tension herself, playing passively for the first time on the first match point. But soon enough she returned to serve and volley to clinch the biggest singles victory of a late-blooming career.

Considering there are players who have basically won Wimbledon with their serve – Richard Krajicek windmills to mind – Maria Sharapova may have to do it the hard way if she is going to triumph again this year. The 2004 champion gave up seven double faults in her straight-sets victory against Johanna Konta on Monday; she followed with eight more in an otherwise routine 6-3, 6-1 dispatching of the Netherlands’ Richel Hogenkamp. These are perturbing stats for the No4 seed.

Of course, Sharapova’s first serve – when it goes in – is formidable; she won 87% of points on it against Hogenkamp. But she has recurring issues with her ball toss and frequently she elects to let it drop and reset. She took her time between deliveries in the Hogenkamp match, perhaps hoping to compose herself, but at times, as she rocked slightly and inhaled deeply, she came across like a vertigo sufferer contemplating a bungee jump. There was a gentle breeze on court but mostly from spectators flapping fans to keep cool.

Asked afterwards if she had ever served three successive double faults before – as she did in the first set – Sharapova replied somewhat tetchily, “I’m sure, yeah.” She went on, “I didn’t find the rhythm in a few of those games. The good thing, after that I regained my timing, is that I started tossing the ball a little bit more consistently. That helped me.”

Sharapova’s serve may have been malfunctioning, but the 28-year-old Russian unleashed any frustrations on her groundstrokes. She hit fiercely off both wings and ended up blasting the compact The 23-year-old Hogenkamp into submission, especially in the second set. Hogenkamp, for her part, had been competitive in the early exchanges; she had obviously decided that Sharapova’s front-to-back movement was something she could exploit and feathered drop shots from all over the court. But this tactic, like anything else Hogenkamp tried, suffered from diminishing returns as the match progressed.

So far, it has been a very cordial draw for Sharapova: world No126 Konta, a wild card, followed by No123 Hogenkamp, a qualifier. It gets a little more testing with Romania’s Irina-Camelia Begu, the 29th seed, in the next round. She will surely improve as the tournament goes on and she needs to.

Serena Williams, Sharapova’s eternal nemesis, looms as a potential semi-final opponent. She played with the unrelenting urgency of a woman who had a prior engagement and no interest in staying on Centre Court for a moment longer than was necessary, beating Timea Babos in 59 minutes to set up a third-round match against Britain’s Heather Watson on Friday.

The world No1 was brutally professional in her 6-4, 6-1 win over Babos, breaking the Hungarian early in both sets and making sure that an upset was never on the cards. Babos, the world No93, and occasionally lobbed a few boulders over the net to keep Williams on her toes, yet the Hungarian knew that she was always fighting a losing battle.

For Williams, it was another small step towards completing a historic calendar slam. No woman has won all four majors since Steffi Graf managed it in 1988 and if any of her rivals were hoping that the added pressure would have a negative effect on Williams in her opening two matches, they are sorely mistaken.

“I’m definitely playing well, which I never say,” Williams said. “I had two really tough matches straight off the bat so I had to pick up my game. She has such a good serve. I really had no option but to play well so far.”

There was intrigue when Williams and her sister Venus – who was also a straight-sets winner in the gloaming against Yulia Putintseva of Kazakhstan – pulled out of the women’s doubles on Tuesday. It later emerged that Serena was feeling sore after beating Margarita Gasparyan in the first round on Monday. Yet she looked fresh against Babos.

Williams is already looking ahead to the challenge of playing Watson after the British No1’s victory over Daniela Hantuchova. “She plays so well on the grass and she loves playing at home,” Williams said. “I never like playing the Brits at home. I really have my I’m just in these Championships to have fun.”

Only here to have fun? Williams was fooling no one.