Select saute or browning setting on a 6-qt. electric pressure cooker. Adjust for medium heat; add 1-1/2 teaspoons oil. When oil is hot, brown one roast half on all sides. Remove; repeat with remaining beef and oil.
Add water to pressure cooker. Cook 30 seconds, stirring to loosen browned bits from pan. Press cancel. Place sweet potatoes, carrots, onion and celery in pressure cooker; top with beef. Combine remaining ingredients; pour over top.
Lock lid; close pressure-release valve. Adjust to pressure-cook on high for 55 minutes. Let pressure release naturally. A thermometer inserted in beef should read at least 145°. Freeze option: Place pot roast and vegetables in freezer containers; top with cooking juices. Cool and freeze. To use, partially thaw in refrigerator overnight. Heat through in a covered saucepan, stirring gently and adding a little water if necessary.