A painful blow was going to land eventually. Lewis Wing delivered it at the start of the second half, a clever finish, as he lifted the ball over three Leeds players and wrong-footed Casilla.
Leeds tried to rally, but Kemar Roofe was denied by a double save from Darren Randolph before Pontus Jansson’s header clipped the post and Bamford put the rebound wide – big chances, costly misses, but Phillips spared their blushes.
Middlesbrough (5-1-3-1): Randolph 7; Shotton 7, Ayala 7, Flint 6, Fry 5, Friend 7; Mikel 8; Wing 7 (Besic 64), Howson 6, Saville 7 (Clayton 78); Hugill 7 (Assombalonga 77).
Subs: Konstantopoulos (gk), Downing, Besic, Fletcher, van la Parra.
Leeds United (4-1-4-1): Casilla 7; Ayling 5 (Shackleton 80), Cooper 5, Jansson 6, Clarke 5 (Hernandez 46); Phillips; Harrison, Klich (Roberts 58), Bamford 4, Alioski 5; Roofe 5.
Subs: Peacock-Farrell, Brown, Davis, Halme.
Referee: Darren England