Eyeing their first three-game winning run in seven years, the three-time reigning wooden spooners shook off game-day injuries to Adam Doueihi (groin) and Samuela Fainu (knee) to take an unlikely six-point lead in Sunday's second half in rainy Campbelltown.
But when Leka Halasima beat Jahream Bula and Jack Bird on a 70-metre tear down the right edge, the Warriors had levelled the scores as the final 10 minutes approached.
The Tigers had been the more clinical side once in position and so would've liked their chances to fire back, until second-rower Alex Seyfarth hit Charnze Nicoll-Klokstad high with eight minutes to play.
Seyfarth could be joined on the match review committee charge sheet by star teammate Jarome Luai, who laid a high tackle on Edward Kosi earlier in the second half.
After Seyfarth's hit, new Warriors halfback Metcalf stepped up and landed a penalty goal from 40 metres in front in greasy conditions.
The win is the Warriors' third on the bounce, leaving a horror round-one loss to Canberra in Las Vegas as a distant memory.
"Everyone lost faith in us pretty quick, but we kept faith in ourselves," said Warriors coach Andrew Webster.
"Every win matters, but there's a long way to go."
The Tigers lost Doueihi in the warm-up and then Fainu in the first half, leaving them with an entirely second-choice left edge for the majority of the game after winger Jeral Skelton (hamstring) was ruled out during the week.
Tigers coach Benji Marshall was hopeful Doueihi could return for next week's clash with Brisbane but was unsure of Fainu's prognosis.
"I'm disappointed for the boys, with the result not going our way," Marshall said.
"But the amount of adversity we had today that we had to get through ... as a coach and a club, we're really proud of the effort, even though we got no favours today. That was pretty obvious."
Marshall would not be drawn to address refereeing decisions as the NRL moves to take a stricter stance on coaches commenting on match officials.
"You were watching the game, you write whatever you think," he told the press.
"I don't want to do what Ricky (Stuart, Canberra coach) did. I don't want to risk getting fined."
Just as the Warriors looked ready to capitalise on the undermanned Tigers, star recruit Terrell May came up with his biggest play yet as a Tiger to swing the contest back to the home side.
Having scored with their first set after the break, the Warriors came within inches of going up by two tries when Bunty Afoa crashed over at close range early in the second half.
May left all onlookers to continue wondering how the Sydney Roosters let him go when he held the big man up.
Warriors half Metcalf passed the ball into touch on the next play and with the Tigers' next possession, they marched upfield to equalise.
Lachie Galvin put boot to ball on a kick for back-up winger Solomona Faataape and, in the set after points, Latu Fainu strolled past Afoa to give the Tigers the lead.
But Halasima's try on the back of a Taine Tuaupiki offload deflated the Tigers, who a blew late chance to steal victory when Faataape kicked the ball into touch working down the left.
Sunia Turuva and Starford To'a couldn't link up on the right on a tear that could have resulted in yet another game-winner, but a third straight win wasn't to be.
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