Drain beets, reserving liquid.
Pour beet liquid into a 1-cup measure and add enough water to make 1 cup of liquid.
Combine sugar, cornstarch, salt, pepper, and vinegar in a 1-quart casserole or bowl.
Stir in beet liquid.
Microwave, uncovered, for 2 1/2 to 3 minutes, on high stirring occasionally, until mixture thickens and is clear.
Add beets and stir lightly.
Cook, covered, for about 3 minutes, on high or until beets are piping hot.