Marcelo Brozovic scored both goals as Croatia opened up a gap at the top of Group I with a 2-0 win over nearest rivals Iceland.
The Inter Milan midfielder opened the scoring in the 15th minute and added his second in added time, with Ivan Perisic's sending-off moments later making no difference to the outcome.
Heading into the match level on seven points with Croatia, it was no surprise to see Iceland sticking to their tactics of sitting behind the ball and counter-attacking at speed, which served them so well at Euro 2016.
However, they were undone by a brilliant strike from Brozovic after just 15 minutes. He played a one-two with Ivan Rakitic before curling a shot past Hannes Halldorsson, with the aid of a slight deflection.
Perisic shot straight at the goalkeeper as the first half ended and the introduction of Real Madrid midfielder Luka Modric for club-mate Mateo Kovacic for the second half saw Croatia pick up the tempo.
Perisic then had another effort blocked as the hosts had to wait until the first minute of added time to secure three points.
Modric released Brozovic to run through and the Inter man kept his footing to beat Halldorsson.
Perisic's late red card for a wild lunge will rule him out of Croatia's next qualifier against Ukraine in March.