Houston Astros legend Craig Biggio is still struggling to believe his son is a successful big leaguer ... telling TMZ Sports, "I'm still having a hard time putting it into words."
"It's incredible," the 53-year-old Hall of Famer says.
24-year-old Cavan Biggio is a rising superstar for the Toronto Blue Jays -- he was one of the team's top prospects in the minor leagues before he got called up just a few weeks ago.
Now, he's hitting in the heart of the Blue Jays' order ... and in his first-ever 125 MLB at-bats, he's got 6 home runs, 24 runs scored, 23 RBIs and 5 stolen bases.