|Przemyslaw Karnowski had a massive 20-point, 13-rebound double-double on Tuesday for Poland|
Both teams had won their opening three games before Tuesday's meeting at the U20 European Championship Men Division B in Pitesti, Romania and it was difficult to separate them.
Even when the Brits took a 12-point, second-quarter lead it was followed by an 8-0 Poland run.
Przemyslaw Karnowski (20 points, 13 rebounds) and Mateusz Ponitka (23 points, 10 rebounds) came up big for the Poles, the latter finishing one fast break with a dunk to close the gap to 78-74 with 43 seconds remaining.
But having led by example once again - with help from Nicholas Lewis who hit 6-of-8 three-pointers for 20 points - it was Van Oostrum, who had the final word.
The point guard hit the final five points from the foul line to take his personal total to 37, but more importantly carry GB across the finish line.
Hungary held on to third spot after a 10-0 sprint finish saw them past Romania 65-53.
Hungary's lead was just two (55-53) heading into the final five minutes but their late surge, punctuated by László Dobos' dunk, proved the difference.
|Joonas Cavén's 34 points could not save Finland on Tuesday|
The other game in Group A saw Luxembourg eliminate the Slovak Republic with their first win, 62-51.
Michal Cekovsky's 12 points and 11 boards paced the Slovak's and helped them to tie at 41 after three.
They led from start to finish, holding a 21-point advantage at half-time before Roberto Mantovani's ‘and-one play' started a 10-0 run.
Cyprus remained at arm's length until closing on an 11-5 run to create a tense finish.
Portugal meanwhile managed to hold on for a 72-63 victory over the Netherlands despite going scoreless in the last five minutes.
The Dutch finished with nine unanswered points but were made to rue five consecutive missed free throws as they slipped to a second straight defeat.
That momentum propelled the Swiss to outscore their opponents 14-8 in the extra period, as Joonas Cavén had 34 points in a losing effort.