This is what is on WGT match play rules :
Yes, Match Play games do affect your score average and your tier ranking. If you play a match play game against a player of higher tier and win the match your score average will be affected which could affect your tier ranking.
I played 4 ranked and scored match plays against Tour Master and Legend. Won all of them but my average remains the same without being affected and till yesterday...... it was working fine...... got my average down to 64........ and now inspite of winning the games the average does not change??????