Newcastle hit Tottenham for four to enliven Champions League race
Spurs' lead over the Magpies is cut to 10 points with six games remaining, but Newcastle have a far easier run-in.
Tottenham conceded five times in the opening 21 minutes of a 6-1 humiliation on their last visit to St. James' Park and were outmuscled and outclassed once more on Tyneside.
Eddie Howe was forced into a switch to a back three due to Newcastle's abundance of injuries in defence.
But the home side's makeshift backline was rarely troubled after Timo Werner skewed an effort wide in a bright start by the visitors.
The game swung decisively in Newcastle's favour thanks to two goals in two minutes thanks to two errors from Micky van de Ven midway through the first half.
The Dutch centre-back has been one of the signings of the season for Spurs, but had an afternoon to forget.
Van de Ven's first slip allowed Isak to smash home from Anthony Gordon's pass to open the scoring.
Straight from kick-off, Van de Ven fell over again as he tried to reach Pedro Porro's backpass and Gordon took full advantage to score his 10th Premier League goal of the campaign.
Newcastle could have had more before the break as Destiny Udogie's last-ditch challenge denied Isak a second before the Swedish striker headed over from a corner.
But any doubt over the outcome was dismissed six minutes into the second period when Isak again beat Van de Ven to Bruno Guimaraes' long ball over the top and slotted home.
Isak is now only two behind Erling Haaland's 19 Premier League goals in the race to win the Golden Boot.
Ange Postecoglou showed his dismay with the Spurs display as captain Son Heung-min was hauled off in a triple substitution before the hour mark.
The visitors also lost right-back Porro to injury to rub salt into the wounds of what could be a damaging day for their hopes of a return to the Champions League next season.
A poor week for English clubs in European competitions means that a place in the top four may be needed to qualify for the Champions League.
Spurs slip behind fourth-placed Aston Villa on goal difference.
But Tottenham have all three of the title contenders -- Arsenal, Liverpool and Manchester City -- to play in their final six games, while Villa face both Arsenal and Liverpool.
Postecoglou warned on the eve of the game that Newcastle's struggles this season show how the demands of European football can drain a squad's resources.
Yet they could still sneak back into the top four with a strong end to the campaign.
Fabian Schar inflicted the final blow when he rose highest to power in Gordon's corner three minutes from time.