With the Riverside clash deep into injury time and the Swans having fought back from 3-1 down to level things at 3-3, Beattie received a pass from fellow substitute Stephen Dobbie on the edge of the penalty area.
Dobbie then continued his run and Beattie tried to complete the one-two but saw his efforts blocked by the lunging tackle of a Boro defender, it was only then that he took the opportunity himself to turn and fire a snap-shot past Jason Steele.
"If I'm honest I tried to play a pass to Dobbs (Dobbie) but it came off the defender and sat up perfectly for me and landed in the bottom corner," he told the club`s official website.
"I said in the dressing room before the game I was desperate to score a tap-in, but I never seem to score those."
Swansea remain firmly in the top six - just one point off the top two - and Beattie added: "Our first job is to secure a play-off place and then aim even higher. First place is our aim but if we fall short then we`ll be happy with second."
Source: PA
Source: PA