Eric Dier gave Tottenham the lead with a header from a corner and Spurs added a second before half-time when Nacer Chadli volleyed in at the back post.
Marko Arnautovic pulled a goal back from the penalty spot after Toby Alderweireld brought down Joselu.
And Diouf secured a point when he got on the end of Stephen Ireland's cross.
It was deserved point for Mark Hughes' side who diligently kept at their task in the second half, even though a comeback looked unlikely after their first-half display.
Tottenham, however, will rue missed opportunities to have secured the points having had the majority of clear-cut chances.