Mauricio Pochettino's side are the first club in the Premier League era not to make a single signing since the introduction of the pre-season transfer window.
That low-key approach has frustrated Tottenham fans, but Alli lifted the gloom with a clinical header to seal at the points at St James' Park.
Despite Tottenham's hard-fought victory, there was another August blank for Harry Kane, who started even though the England striker had only returned to training on Monday following his notable World Cup exploits.
Ashley, the club's notoriously parsimonious billionaire owner, saw fit to spend 90 million pound (10.6 million euros, $11.5 million) on the ailing department store group House of Fraser. Meanwhile his Magpies posted a net transfer profit of 20 million pound, despite the arrival of seven new signings, the most expensive of which, Japanese international forward Yoshinori Muto, cost 9.5m pound from German side Mainz.
-- Deft header --
Tottenham fans appear rather less dissatisfied, despite their club failing to make a single addition to Pochettino's squad since the end of last season.
Such inactivity proved no impediment as the visitors rode their luck to seal a repeat of their opening day victory at St James' Park 12 months ago.
The visitors took an eighth-minute lead when Christian Eriksen's corner was headed towards goal by Davinson Sanchez, allowing fellow defender Vertonghen to find the net off the underside of the bar with a deft glancing header which crossed the line before Martin Dubravka was able to claw the ball back.
Newcastle were level within three minutes when Sanchez and Vertonghen were caught ball-watching as Matt Ritchie sent over an inviting centre from the right which Joselu headed into the bottom corner of the net past an exposed Hugo Lloris.
With momentum on their side and a full-house roaring them on, Benitez's side looked set to build from a position of strength.
But thanks to more questionable defending, their parity lasted just seven minutes. Tottenham's second goal was simple in its construction and should have been comfortably dealt with.
Newcastle allowed Alli a free run at the far post to send a precise header back across Dubravka into the far corner from Serge Aurier's inviting cross, which was whipped in from the right.
An increasingly open second period surprisingly failed to produce further addition to the score, as both goalkeepers excelled.
Dubravka saved well to deny Alli when the midfielder deflected Kane's mis-hit shot towards goal.
Newcastle's Slovakian keeper provided an even better stop to keep out a well-struck effort from Moussa Sissoko.
Not to be outdone at the other end, Lloris stood up well to block Ayoze Perez's shot.
Mo Diame and substitute Salomon Rondon both struck the woodwork as Newcastle pressed for what would have been a fully deserved equaliser, but Tottenham held firm.
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