LONDON - Colourful US star Bethanie Mattek-Sands suffered a horrific knee injury at Wimbledon on Thursday which left her screaming in pain and heartbreakingly pleading for help.

The distressing drama on Court 17, where the 32-year-old lay stricken for at least 20 minutes, pushed the title campaigns of Novak Djokovic and Roger Federer onto the sidelines.

"Please help me! Please! Please!" screamed Mattek-Sands as she clutched her right knee after collapsing running to the net in the first point of the deciding set against Romania's Sorana Cirstea.

The women's tour said Mattek-Sands had suffered a serious knee injury. "It is an acute knee injury and she has gone straight to hospital," the WTA Insider tweeted.

Mattek-Sands's husband Justin tried to console his wife as medics arrived, while Cirstea, who rushed over the net to help, was visibly distraught. After lying prone on the ground screaming in pain as she waiting for medical assistance, Mattek-Sands was eventually stretchered away.

Her doubles partner, Lucie Safarova, with whom she shares the world number one ranking as well as four Grand Slam titles, also arrived at the scene in tears. The terrible scenes on Court 17 dominated the fouth day of the tournament.

DJOKOVIC CANTERS THROUGH: Earlier Novak Djokovic shrugged off sweltering 30-degree heat to breeze past outclassed Adam Pavlasek 6-2, 6-2, 6-1 and reach the third round. The three-time champion brushed aside the 136rd-ranked Czech on Court One to make the last-32 for the ninth year in succession.

Djokovic, the second seed whose shock third round loss to Sam Querrey at Wimbledon 12 months ago precipitated a worrying decline in form, will next face Ernests Gulbis. "It was a very warm day, it wasn't easy to play point after point and some long rallies," said Djokovic as his comfortable Wimbledon continued following a first round in which opponent Martin Klizan had retired hurt after just 40 minutes. "But overall, from the very beginning I managed to impose my own rhythm and play the game I intended to play."

Gulbis sprang a Wimbledon surprise as the world number 589 defeated former US Open champion Juan Martin del Potro 6-4, 6-4, 7-6 (7/3). The 28-year-old Latvian was ranked in the top 10 in 2014 -- the year he beat Federer en route to the French Open semi-finals.

Since then, Gulbis has slumped badly and his Wimbledon opening round win over Victor Estrella, was his first on tour in 13 months, a decline which has seen his ranking crash to his lowest position in 12 years. Bulgarian 13th seed Grigor Dimitrov, a semi-finalist in 2014, saw off Cypriot veteran Marcos Baghdatis 6-3, 6-2, 6-1 while pint-sized Dudi Sela stunned giant American John Isner 6-7 (5/7), 7-6 (7/5), 5-7, 7-6 (7/5), 6-3. Bernard Tomic may have been knocked out but the Australian was still making waves on Thursday when he was fined $15,000 after claiming he was "bored" during his lacklustre defeat to Mischa Zverev. Tomic, who was accused of "unsportsmanlike behaviour" had also admitted he called for the trainer even though he was not injured to try to disrupt his opponent's momentum.

Russia's Daniil Medvedev was slapped with a $14,500 fine after a series of disputes with umpire Mariana Alves during his five-set loss to Ruben Bemelmans in the second round. Medvedev ended the match by throwing coins in the direction of umpire's chair although he insisted the bizarre gesture was not meant to imply that the official was corrupt.

FEDERER PREPARES, PILSKOVA FALLS: Later Thursday, third seed Federer was to continue his campaign for a record eighth Wimbledon title against world number 79 Dusan Lajovic. Women's top seed Angelique Kerber, the runner-up to Serena Williams in 2016, tackles Belgium's 88th-ranked Kirsten Flipkens, whose best performance at the majors came at Wimbledon in 2013 when she made the semi-finals.

Plískova, the world No3 and the tournament favourite when her second-round match against Magdalena Rybarikova began, crashed out in three sets. Czech hopes of an emotional third title here for the her compatriot Petra Kvitova were dashed with defeat. Now Plíšková has snatched defeat from the jaws of victory. At one point she was a set and break up before Rybáriková prevailed 3-6, 7-5, 6-2. Rybáriková, 28, the world No87, produced some stunning shots in a compelling contest on Centre Court.

Former US and French Open champion Svetlana Kuznetsova, seeded seven, took her career record over fellow Russian Ekaterina Makarova to 7-1 with a 6-0, 7-5 win. Kuznetsova next faces Slovenia's world number 265th Polona Hercog, who reached the third round at a Slam for the first time since 2010 with a 6-7 (2/7), 6-2, 6-2 win over Varvara Lepchenko of the United States.

Agnieszka Radwanska, the 2012 runner-up, saved two match points to see off Christina McHale 5-7, 7-6 (9/7), 6-3.

On late Wednesday, Andy Murray, Rafael Nadal and Venus Williams breezed into the third round at Wimbledon on Wednesday, while fellow former champion Petra Kvitova tumbled out. Williams, Kei Nishikori and Johanna Konta had to grind their way into the last 32, while new mum Victoria Azarenka continued her comeback bid for Grand Slam glory.

Dustin Brown, the dreadlocked German with Jamaican roots, knocked out Nadal in the second round two years ago at the All England Club. However, world number one Murray was not caught out by his extrovert drop shots, racing to a ruthless 6-3, 6-2, 6-2 victory on Centre Court.

Fourth seed Nadal, fresh from winning a historic 10th French Open, had a comfortable ride against fellow left-hander Donald Young of the United States, the Spaniard winning 6-4, 6-2, 7-5. He faces Russian 30th seed Karen Khachanov next. Two-time champion Petra Kvitova, the bookmakers' title favourite, lost 6-3, 1-6, 6-2 to Madison Brengle of the United States.

Troubled US five-time champion Williams survived a scare against Chinese rising star Wang Qiang, eventually winning 4-6, 6-4, 6-1. Williams is trying to concentrate on tennis against the backdrop of impending legal action back home over a fatal car crash. Williams next faces Japan's Naomi Osaka, who ousted Czech 22nd seed Barbora Strycova. Nishikori dug deep to keep his Wimbledon hopes alive as the Japanese ninth seed ground out a 6-4, 6-7 (7/9), 6-1, 7-6 (8/6) win over Ukrainian qualifier Sergiy Stakhovsky. He next faces Spanish 18th seed Roberto Bautista Agut.

In the women's draw, second seed Simona Halep went through in straight sets, while fellow seeds Elina Svitolina (4th) and Dominika Cibulkova (8th) also made it. French Open champion Jelena Ostapenko joined them in the third round with a late evening three-set win over Canadian qualifier Francoise Abanda.