The centre-backs faced off at the Ricoh Arena, with both turning in excellent defensive performances, as they each helped their team to a clean sheet.
Stephens and the rest of the City back-line were impressively able to contain the division’s top scorer, Nicky Ajose, as they blanked the opposition for the second game running.
Turnbull’s display also played a crucial part in the Robins extending their unbeaten league run to seven matches.
Coventry nearly won the game in the dying stages, but Darius Henderson’s half-volley was well saved by Swindon keeper Tyrell Belford.
City are now eighth in the table, two points off the play-offs, while the Robins are six points further back, in 14th position.
Climbing back into the top six in League 1 was winger Lloyd Isgrove, who helped Barnsley to a 2-0 win away to Fleetwood Town.
Isgrove played 89 minutes, as the Tykes claimed victory for the 13th time in 17 games, via a Joe Davis own goal and a Josh Scowen effort.
Southend United and on-loan Saints striker Sam McQueen are also very much in the League 1 play-off race.
They drew 1-1 at home to high-flying Gillingham, although will be disappointed not to have taken three points after Anthony Wordsworth’s first-half goal was cancelled out after the break by Luke Norris.
McQueen came off the bench in the 76th minute, nearly setting up Tyrone Barnett for the winner with a good low cross that the forward couldn’t convert.
Southend are up to ninth in League 1, three points behind sixth-placed Barnsley.
In League 2, defender Jason McCarthy is also chasing a play-off spot with Wycombe Wanderers, who remain well in the hunt after a hard-earned 1-1 draw at Carlisle United.
Sam Wood opened the scoring for the Chairboys, with a well-placed header in the 12th minute, but Carlisle equalised midway through the first half when Charlie Wyke tapped in.
Wycombe could have claimed all three points, but Joe Jacobson saw a first-half penalty saved. McCarthy, who played the full game at right back, then helped the visitors hold onto a point that leaves them eighth in the table, two points behind Leyton Orient, who occupy the final play-off spot.
In the Championship, Gastón Ramírez is also challenging strongly for promotion with Middlesbrough, who won a crucial home game with Hull 1-0, thanks to Dave Nugent’s header in added time.
Ramírez played 89 minutes of the match before being substituted, as Boro held onto third place in the second tier, one point behind Brighton in second, but with a game in hand on the Seagulls.