Pakistan's Fakhar Zaman plays at Lord's Cricket Ground in London on Sunday. Saeed Khan/AFP

Pakistan captain Sarfaraz Ahmed won the toss and decided to bat first in a must-win World Cup clash against fellow strugglers South Africa at Lord's on Sunday.

Pakistan and South Africa both need a victory to keep their slender hopes of qualifying for the semi-finals alive.

With only one win apiece, neither side have any margin for error in the first match of the tournament to be staged at Lord's, Cricket's spiritual home, in north London.

Sarfaraz backed his team to put up a big score in warm conditions, which would allow them to pile pressure on the Proteas' batting line-up in the chase.

"It looks like a good pitch but we'd like to put runs on the board and hopefully defend it," he said.

South Africa's players huddle at Lord's Cricket Ground  in London on Sunday. Saeed Khan/AFP

"We're focusing on this match and not other things. It's an important game for us."

South Africa captain Faf du Plessis claimed he would have bowled first anyway if he had won the toss.

"I'm happy to be chasing - I would have bowled first, so it's a good toss to lose," he said.

"There's always pressure. Hopefully we'll see an exciting game today with both sides playing their best Cricket.

"I think we've been getting better in every game. Hopefully today is another opportunity."

Pakistan made two changes as Shoaib Malik and Hassan Ali were left out, with Shaheen Afridi and Haris Sohail coming in.

South Africa were unchanged from their narrow defeat against New Zealand.

If Pakistan win they will go to five points with three games to play in the race to finish in the top four.

Spectators cheer of the 2019 Cricket World Cup group stage match between Pakistan and South Africa at Lord's Cricket Ground in London. Saeed Khan/AFP

A South Africa success would move them to five points, but they will have only two games left to catch fourth-placed England, who have eight points from six games.

Teams

Pakistan: Fakhar Zaman, Imam-ul-Haq, Babar Azam, Mohammad Hafeez, Haris Sohail, Sarfaraz Ahmed (capt/wkt), Imad Wasim, Shadab Khan, Wahab Riaz, Mohammad Amir, Shaheen Afridi

South Africa: Hashim Amla, Quinton de Kock (wkt), Faf du Plessis (capt), Aiden Markram, Rassie van der Dussen, David Miller, Andile Phehlukwayo, Chris Morris, Kagiso Rabada, Imran Tahir, Lungi Ngidi

Umpires: Joel Wilson (WIS), Kumar Dharmasena (RSA)

TV umpire: Chris Gaffaney (NZL)

Match referee: Ranjan Madugalle (SRI)

Agence France-Presse