Tough problem...
I have had diabetes for over 20 years and have been using an insulin pump for nearly 8 years. I have been playing tennis off and on for over 40 years. I still play competitively.
I think these problems in managing your blood sugar levels are perhaps the most perplexing aspect of living with diabetes. We all learn how food and exercise impacts our blood sugar levels. To a large extent we know how to control this within reason. However, when it comes to physcologically induced blood glucose swings (e.g. stress, hormones, adrenaline) it's rather mysterious. Often, it's extremely hard to predict these events and how to counter them (i.e. bolus amounts, etc.). Furthermore, hormonal and adrenaline can temporarily alter your insulin sensitivity, further compounding strategies to control things.
Fortunately in your case you have a pretty good idea as to what is causing it and perhaps the remedies for dealing with this anxiety and stress are the same as for non-diabetics. In other words, you need to learn to relax and treat these matches as if they are just another form of practice. I realize this can be difficult to pull off, but I don't see any other option. Furthermore, if you are able to do this your results will be better and I suspect that your glucose levels will behave better.
Recently, there have been significant advances in Continuous Glucose Monitoring (CGM) systems. I have been a trial patient for this technology and can provide you with more information about how it works, the pro's and con's, and whether you are a decent candidate for this technology. The primary downside is the cost of the sensors. If your family has good health insurance then most of the costs may be covered.
Shoot me an email if you want to learn more about CGM's.
