Cook pasta according package to directions. Drain, but reserve about 1/2 cup water.
Whisk cream cheese with pesto and about 6 Tbsp pasta water until creamy. Adding more or less water will produce thinner or thicker sauce. Pour over drained tortellini and toss to combine.
Serve immediately. Serving suggestion (optional): sprinkle with some chopped parsley, roasted sunflower seeds and grated Parmesan cheese.