The pair have 14 goals between them so far this season, helping the promoted side to a top-half position.
The Hornets have surprised many since being promoted from the Championship. Quique Sanchez Flores' men sit ninth in the table, nine points clear of the bottom three.
And Ighalo explained that the blossoming partnership between him and Deeney is one of the reasons for their success, and will be imperative to their hopes of securing a second successive season at this level (via the London Evening Standard).
"We played with each other in the Championship last season and we were great. I scored 20 and he scored 21. We've been working hard every day and I know we've been causing defenders serious problems. We know if we keep fit and doing this we'll stay up," he said.
The 26-year-old is the club's top goalscorer this term with nine strikes, including the winning goal against Swansea, as well as braces against Newcastle and West Ham.
Meanwhile, Deeney has bounced back from nine goalless games to begin the campaign, with a run of five goals in their last six matches.
As Ighalo alluded to, Watford's hopes of staying up may well depend on whether the pair can stay fit. Only three of the club's goals have come from other players this season, while the manager has very few attacking options with Premier League experience to call upon, should either pick up an injury.