"The kid's really good," Blake told the partisan Texas crowd after the match. "There's a lot of good things in store for him."
Blake, who won the final eight points of the match -- the last one a deftly placed low forehand crosscourt volley winner -- drew a glare from the youngster at 2-2 in the final set. The look came after the second-ranked American player clobbered Harrison with the ball after he had drawn Blake to the net on a drop shot.
Later, Blake said he knew the importance of the point. He was down love-15 on his serve.
"I didn't want to lose it and sometimes that's the easiest way to win the point," Blake said. Jokingly he added, "A little souvenir to say, 'Welcome to the ATP.'"
Blake broke Harrison in the first game of the match and three other times in the first set. Harrison hung in, though, and was able to take the top seed's serve twice in the opening set.
The youngster said he respected Blake's offensive style.
"So we were going to try to take that away but that didn't work out so well whenever you miss as many first serves as I did," Harrison said. "I was letting him step around and attack a lot."
With Blake up 4-1 in the first set, Harrison ran off nine straight points, including four to break serve. The youngster said he thought Blake relaxed a little.
"As soon as he relaxed, I ... tried to get some momentum, which I was able to do, hit a little streak there where I won a few points in a row," Harrison said. "Then he regained his focus" and closed out the set.
Blake will face fifth-seeded Agustin Calleri of Argentina on Friday. Calleri dominated fellow South American Paul Capdeville 6-2, 6-1. Blake leads the series with Calleri 2-1. Blake won their only meeting on clay -- last year in Germany in three sets.
Calleri was all over Capdeville's serve, breaking him twice in each set -- two of those coming in the Chilean's initial service games. The Argentine converted on four-of-15 break-point chances.
In the fourth game in which Calleri broke Capdeville's serve, Calleri whipped a sharply angled crosscourt forehand passing shot that was well beyond his opponent's reach to make it 5-1 in the second. The Argentine won the match when Capdeville missed a forehand wide.
Capdeville had only one break chance in the match. There were five deuces in that game, the fifth of the second set, but the Chilean failed to convert when he netted a low backhand. Calleri closed the game out with an ace.
In other matches, American Wayne Odesnik beat Dudi Sela of Israel 6-3, 7-5 to advance to the quarterfinals. Odesnik's opponent Friday will be Sergio Roitman of Argentina, who beat Russian Igor Kunitsyn 6-3, 7-6 (3).
Spaniard Marcel Granollers-Pujol took out Peter Luczak of Australia 6-3, 6-2 to reach the quarterfinals. Granollers-Pujol will play Friday against Brazilian Marcos Daniel, who beat Nicolas Massu of Chile 7-6 (3), 6-2 to advance.
In another quarterfinal pairing Friday, third-seeded Mardy Fish of the will play No. 8 seed Spaniard Oscar Hernandez. The two players have played only once before -- in a non-ATP tournament in Bermuda in 2006. Hernandez won 6-4, 7-6 (4).