Alas, five-eighth Tane Edmed missed with a drop-goal attempt of his own before Valetini sealed a famous first-time victory for the Drua over the Waratahs.
The Pacific Islanders had lost all four previous meetings between the sides. But, as evident by their round-two ambush of the defending champion Crusaders, Churchill Park is proving a fortress for visiting teams.
The visitors had made a flying start to lead 10-0 inside the opening 10 minutes. Flanker Charlie Gamble put hooker Mahe Vailanu over in the fourth minute from a lineout win before Edmed converted from the sideline and slotted a penalty goal shortly after.
But just as the Waratahs threatened to pull off another runaway win over the Drua, the inspired home side produced a four-try blitz in the space of 20 minutes to seize control.
Olympic sevens gold medallist Iosefo Masi was at the centre of the fightback. First, he bamboozled World Cup trio Izaia Perese, Mark Nawaqanitawase and Max Jorgensen to score under the posts.
Then, either side of the softest of tries from Drua halfback Frank Lomani from a lineout, Masi collected his second and third. He out-paced the defence for his second and snuck through a hole close to the line for his third as the Drua stormed to a 26-10 halftime lead.
Perese and centre partner Joey Walton combined well to put Gamble over shortly after the break to ignite the Waratahs’ comeback. Tevita Ikanivere replied with the Drua’s fifth try before Walton scored to again reduce the deficit to nine points.
With the hosts down to 14 men after replacement forward Kitione Salawa was yellow-carded, the Waratahs pulled to within a converted try when Vailanu bagged his second.
It was all level at 36-36 when Lachie Swinton crashed over with 15 minutes remaining.
But Valetini’s late intervention consigned Darren Coleman’s side to their most crushing defeat yet in this campaign of frustrating near misses.
Nawaqanitawase’s milestone 50th game was a largely forgettable one. Playing in front of his Fijian father’s family, the classy winger spent 10 minutes in the sin bin for a deliberate knockdown to prevent a Drua try in the shadows of halftime and was offered few chances to showcase his silky attacking game.