The Phoenix (5-3) overcame an early 8-0 deficit and climbed back to take the lead on a Carrington Love 3-pointer, which sparked a 10-0 run to make the score 60-52 midway through the second half.
South Dakota (3-6) cut the lead to three multiple times, but couldn't pull any closer. A Trey Norris three-point play made the score 86-83 with 19 seconds left, but Green Bay countered with a Greg Mays dunk. Sykes hit a free throw following a Brandon Bos layup for the final margin.
Green Bay had five players score in double figures. Mays scored 15 points, and Jordan Fouse finished with 11 and 14 boards.
Bos scored 19 points, and Trevor Gruis contributed 16 with eight rebounds to lead the Coyotes.
Forward Kennedy Meeks, who has averaged 9.4 points and 6.5 rebounds at North Carolina, has pulled out of the NBA draft and will return to the Tar Heels.
Cal big man Ivan Rabb could have been selected in the top 10 of the NBA draft. Instead, he's returning to Berkeley to make himself, and the Golden Bears, stronger.
Devin Williams' decision last month to sign with an agent and enter the NBA draft has left West Virginia in a tough spot.