Turning Point: Poland led 73-71 with 1:09 remaining and outscored Portugal 8-2 the remainder of the way.
Game Hero: Poland's Lukasz Koszarek had seven of his game-high 18 points in the final quarter.
Stats Don't Lie: Poland outrebounded Portugal 39-25.
Portugal played their hearts out but it wasn't enough as Poland secured an 81-73 victory for their first win in Group A at the EuroBasket on Friday.
Poland's Lukasz Koszarek had seven of his game-high 18 points in the final quarter.
"This is a very important win for us," said Koszarek. "We knew how important this game was for us and for them and it was a battle from start to finish.
"Thankfully, we held on for victory."
Mario Palma's side pushed Poland to the limit and only trailed 73-71 with 1:09 remaining but ran out of steam.
Portugal led 36-29 at the break but failed to make a single basket in the first six minutes of the third quarter while the Poles scored 12 unanswered points to go in front, with four different players contributing in that stretch.
Miguel Miranda's layup halted the long drought for Portugal and they outscored their opponents 13-7 to go into the final frame with the game knotted at 49-49.
Midway through the final quarter, Portugal led 61-60 but Poland outscored them 13-4 over the next three minutes to go in front, 73-65.
Antonio Tavares and Jose Costa buried consecutive threes to cut the gap to 73-71 before Poland went on a final 8-2 run.
Tavares and Costa had 13 points apiece in defeat.