The 22-year-old stepped into the departed David Wheater's shoes for the 1-1 home draw with Preston and did enough to convince his manager he can do a job for the club.
Mowbray told Boro's official website: "I thought Seb was outstanding. It's a compliment to him that I don't really notice him.
"He has done exceptionally well whenever he's been called on - and he looks like a centre-half now as he has stitches in a head wound.
"The bottom line is that if he plays like he did on Saturday, then he will earn an extended run in the team."
Source: PA
Source: PA