Pakistan and Sri Lanka head into their concluding group Champions Trophy group match knowing it's a virtual 'quarter-final' after producing two of the tournament's biggest upsets so far.

Monday's match in Cardiff has the look of a 'dead rubber' about it after Pakistan suffered a 124-run thrashing by arch-rivals and Champions Trophy title-holders India in their opening Group B match.

But now, in the words of Sri Lanka captain Angelo Mathews, the final round of fixtures in this pool are a "must-win game for all of us in the group".

Sri Lanka too suffered an almost as heavy a loss in going down by 96 runs to South Africa first up in a tournament featuring the world's top eight one-day international teams.

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But Pakistan bounced back to beat top-ranked South Africa by 19 runs on Wednesday at Edgbaston -- the ground where they had succumbed to India just days earlier.

And 24 hours later, Sri Lanka had a winning return at the Oval courtesy of a stunning seven-wicket success against India.

Having conceded 319 for three against India, Pakistan restricted South Africa to 219 for eight.

After the spinners did the initial damage, paceman Hasan Ali took three for 24 in eight overs.

Babar Azam and Shoaib Malik then got Pakistan ahead of their required run-rate to secure a 19-run win under the Duckworth-Lewis-Stern method when rain stopped play with their side 119 for three off 27 overs.

Trying to explain the turnaround in his team's fortunes, Pakistan captain Sarfraz Ahmed said: "We had a good bowling meeting.

"We took wickets. If you take wickets, every good team feels under pressure."

Pakistan were also inspired by playing in front of a partisan crowd, something they have rarely enjoyed since a 2009 terror attack on the Sri Lanka team bus in Lahore led to them playing most of their major matches overseas.

"That is a feeling we miss, not playing in Pakistan," said Sarfraz.

"Maybe that was a difference, the crowd was supporting us and that's why the players were boosted."

Sri Lanka too did not lack for support at the Oval as they turned the tables on India in dramatic fashion.

Set 322 to win, Sri Lanka knocked off the runs with eight balls to spare thanks to contributions from Kusal Mendis (89), Danushka Gunathilaka (76) and all-rounder Mathews (52).

"It's one of the top wins, to beat India," said Mathews. "The bowlers did brilliantly to restrict India to 321. It was a very chaseable target.

"Not many people expected us to win and that took a lot of pressure off us."

Mondays match is the only Group B fixture taking place in Cardiff.

Pakistan do have some recent knowledge of the ground beaten England there by four wickets in a one-day international last year.

Left-arm spinner Imad Wasim starred with both bat and ball in that Cardiff clash and he will hope for more success upon on his return 'home' -- he was born in the nearby town of Swansea.