With Wests Tigers' impressive upset win over then-ladder leaders South Sydney on Saturday, they can now officially lay claim to the title of 2018 giant-killers.

According to NRL.com Stats, Ivan Cleary's men are now 5-1 against the heavyweight top-four sides of the Storm, Dragons, Rabbitohs and Roosters.

Their five wins versus current top-four sides is the best in the league; the next best record belongs to the Dragons, who are 3-2 versus their fellow top-four teams. The eighth-placed Warriors are the only club to have played more matches against those four teams and have a respectable 3-4 record against them.

The one real blot on the copybook of the fourth-placed Roosters, who produced their slickest 80 minutes of the year against Manly on Sunday, is that they are yet to beat any of the three teams above them; they are 12-3 against the 12 teams below them but have lost their one meeting against each of the Dragons, Rabbitohs and Storm.

The Storm, Rabbitohs and Panthers all have two wins and a loss against the current top four and are the only remaining teams with a winning record. The Bulldogs, Knights (both 0-6), Cowboys (0-5), Roosters (0-3), Eels and Raiders (both 0-2) are the six teams who are winless against top-four opposition. The remaining teams, Brisbane (2-3), Cronulla (1-4) and Manly (1-5) have each beaten top-four opposition this year.

The Tigers' giant-killing run started early with a surprise double blow against the Roosters and Storm in rounds one and two. It was arguably a pretty good time to get both clubs as they were still piecing together new combinations, and that's according to Cleary himself.

They proved it was no fluke in round five, travelling down to Melbourne to knock off the defending premiers for the second time in a month, before a mid-season slump of just two wins between round six and round 17 (including losses to the lower-ranked Eels, Titans and Knights). That run also included their only loss against a top-four team with a narrow 16-14 two-tries-apiece loss to the Roosters at Allianz Stadium in round 13.

They snapped that dry spell in impressive fashion with wins over the Dragons and Rabbitohs in the past fortnight to keep their finals hopes alive, and it's probably fair to say the current top four would be relieved to see the Tigers lose a few more games to bottom eight sides in the run home given their propensity for upset wins.