A dreadful start to the season saw Bilic's side lose their first three games to sit bottom of the Premier League.
But everything changed after Bilic's now famous press conference ahead of the crucial 2-0 win over Huddersfield when he bit back at Sullivan who - as far as fans were concerned - had publicly 'thrown him under the bus' with comments about the manager's reluctance to sign on the face of it two quality players before the transfer deadline.
'He likes to talk' was the line which set the tempo in that press conference.
Bilic went on to demand a journalist in attendance read out the derogatory name aimed at Sullivan and Gold by their Sporting Lisbon counterpart in the fallout from West Ham's doomed bid for William Carvalho and proceeded to laugh, saying he found it funny.
It was billed as his last stand, gallows humour from a man who knew what was coming.
Whether that was the case or not, the saga stirred something in Bilic that had been missing since the club's superb record-breaking final season at Upton Park.
The spark was back, that mean streak needed to keep multi-millionaire footballers in check.
Bilic has been accused of being too nice, too much of a yes man to the owners, too pally with players.
Well whether it was deliberate or not that changed too.
In an interview with Sky Sports the boss reacted sternly to suggestions he was 'too nice' and a soft touch.
Bilic ripped up his team shape, told his players in no uncertain terms things had to change.
Against Huddersfield with the game still in the balance at 1-0 Bilic took the unpopular decision to substitute fans' favourite Javier Hernandez for the less well-liked Andre Ayew.
Jeers rang out around the London Stadium, it was a decision which could have cost him his job had the Terriers come back into the match.
But Bilic stood in the pouring rain defiantly that night and watched as Ayew scored the second to seal the club's first three points of the season.
Emboldened Bilic then demanded more from his players after they worked hard for a 0-0 draw at West Brom. On the touchline he was taking on Tony Pulis, the referee, the fourth official... anyone who fancied it.
He publicly called on record signing Marko Arnautovic to repay his teammates and the fans for his silly sending off earlier this season.
He told Andy Carroll in no uncertain terms he will not be swayed by the striker's very public show of frustration at being substituted.
For the first time he said publicly that Diafra Sakho's attitude previously stank the place out.
Bilic also insisted Chicharito will have to sacrifice himself and play out wide for West Ham to benefit the team.
Arnautovic responded by orchestrating the club's 3-0 win over Bolton in the cup in midweek.
Bilic's response? He was far from happy and said the player can and must do more and even accused him of getting lazy.
It all points to a more ruthless Bilic and one West Ham fans will hope is here to stay.