Japan international Okazaki is the top scorer in the German top flight with five goals from as many appearances, but sat out the visit of Hoffenheim due to a calf problem.
Mainz were unable to find the target in his absence and may consider themselves somewhat fortunate to have claimed a point after Markus Gisdol's men enjoyed marginally the better of a low-quality encounter, striking the woodwork in the second half.
A victory for either side would have lifted them to the top of the Bundesliga ahead of Bayern Munich's clash with Cologne on Saturday, but the stalemate ensures Pep Guardiola's men retain top spot.
Karius was twice called into action to deny Anthony Modeste and then pulled off a fine stop, diving to his right to keep out an effort from Roberto Firmino.
At the other end, Oliver Baumann had to react well to save a lobbed effort from Filip Djuricic following a swift counter-attack.
