Do you regularly have long rallies dashing from sideline to sideline?
For most, there are periods of a match with short points where you are not getting an aerobic workout.
So you may not get the aerobic workout from just playing to prepare you for the several times during the match where successive long points will really test your reserve.
If your goal is maximum anaerobic fitness to face any situation on court, you probably will have to do some off court HIIT.
Don't forget HIIT can involve doing agility drills at maximum speed to work on your changing direction.
USTA agility drills: http://assets.usta.com/assets/1/USTA...oc_437_269.pdf
But don't beat yourself up about this. Enjoy your tennis and decide whether an extra hitting session of nonstop play would be better overall for your tennis skills and meet your conditioning needs.