After losing their opening six games of the season, the Eels have recorded back- to-back wins to breathe life into their flailing campaign.
However the victory was quickly soured by fears second-rower Tony Williams tore his ACL for the second time in a year.
"I don't think it's real good. He needs to have scan tomorrow, but I've been told that it's ACL," Eels coach Brad Arthur said after the match.
In a closely-fought contest in which the lead changed hands seven times, it was Eels second-rower Manu Ma'u who stood out as the unlikely hero with a try and try assist in the second half.
The Eels were down by four points with 11 minutes to go on Sunday when Ma'u powered over off a Corey Norman pass to claim the match-winning try in front of a crowd of 17,555.
The result means the resurgent Tigers have lost consecutive matches for the first time this season, and leaves them outside the top four for the first time in a month.
Parramatta remain in last spot but are level with Manly, Canterbury and North Queensland to move within two victories of the top eight.
After both teams traded penalty goals early, the Tigers broke the game open when Esan Marsters burst into the backfield and found a supporting Corey Thompson in the 25th minute.
But the defensive lapse only spurred the Eels into gear, crossing twice in five minutes through Bevan French and Michael Jennings to steal the ascendancy.
French soared over opposite winger David Nofoaluma to claim his first try of the season, before Jennings took a sublime Mitchell Moses offload on the other side of the field.
Another Marsters penalty on the stroke of halftime reduced the Eels' lead to two at the break, before a piece of Luke Brooks magic not long after the resumption gave them the lead.
Possessing what Nine Network commentator Phil Gould described as the best no- look pass in the league, the Tigers' halfback put Matt Eisenhuth between the posts untouched in the 45th minute.
A late Ma'u offload allowed Brad Takairangi to steal back the advantage, which they held for just five minutes before Marshall seized back the initiative by backing up Mahe Fonua.
However, the Eels claimed the lead for good on Mau's rampaging run, and held on to back up their breakthrough win last week over Manly.