The defending double world champion and runaway leader of this year’s title race wound up just 0.011 seconds clear of the rookie Australian after the final runs on another rain-affected day's action in the Ardennes forests.
Carlos Sainz was third for Ferrari ahead of team-mate Charles Leclerc, Lando Norris in the second McLaren and Alpine's Pierre Gasly with seven-time champion Lewis Hamilton showing early pace taking seventh place on the grid for Mercedes.
Sergio Perez was eighth in the second Red Bull ahead of Esteban Ocon's Alpine and George Russell, who inadvertently baulked Mercedes team-mate Hamilton’s final lap.
It was a bad morning for Aston Martin as Fernando Alonso celebrated his 42nd birthday by exiting the second qualifying session without recording a flying lap because team-mate Lance Stroll crashed and red-flagged the session.
"It was pretty difficult out there," said Verstappen.
"Similar to yesterday. We were later onto the slick tyres and stayed calm and it didn't take risks. It was super-slippery."
Piastri admitted: "It's obviously really disappointing to miss out on pole just 11 thousandths of a second, but I am proud to be on the front row – I'll say it did it on purpose because of the run we get into Turn Five!"
Verstappen also topped qualifying on Friday for Sunday's main event but a grid penalty for a change of gearbox demoted him to sixth.
Verstappen leads the drivers' championship by 110 points from teammate Perez.
The session was delayed by 35 minutes due to heavy rain, a move that followed widespread concern about the risks involved in running in wet conditions after the death, earlier in July, of Dutch teenager Dilano van 't Hoff and, in 2019, of French F2 racer Anthoine Hubert.
Hamilton, who expressed confidence in the FIA’s decisions on race and track safety, was the first driver out for the opening part of the 'sprint shootout', his car throwing up a high plume of spray in its wake.
The seven-time champion clocked 2:02.297 as a starter to SQ1 as conditions slowly improved, lap times tumbled and, perhaps understandably on his 42nd birthday, Alonso was last to join the fray.
Red-flagged
Everyone ran on intermediates for the frantic 12 minutes that ended with Verstappen on top ahead of Hamilton and Alonso while Yuki Tsunoda, Valtteri Bottas, Kevin Magnussen, Zhou Guanyu and Nico Hulkenberg were eliminated,
For Haas, it was a double disappointment made worse by the self-inflicted exit of Hulkenberg, held up in a pit-stop when the front jack broke. "Very interesting execution there," said the dry-humoured German.
The second segment began with Daniel Ricciardo first out in his Alpha Tauri and Norris going top, the conditions encouraging Stroll to switch to slick mediums.
It was a costly move as he admitted. "It's too early," he reported before crashing heavily into the barriers, destroying the front of his Aston Martin.
The session was red-flagged and did not resume, leaving Ricciardo, Williams pair Alex Albon and Logan Sargeant, Stroll and team-mate Alonso facing elimination, without a chance to respond. Verstappen was fastest again, ahead of Hamilton.
The final six-minute session began with all ten drivers on soft slick tyres on a drying circuit.
Gasly and the Ferraris, led by Sainz, set the pace, but it was Verstappen in 1:49.056 who took pole position to beat Piastri’s late lap by 0.011.
