Ipswich reclaimed second spot in the Championship with a 0-0 draw at West Brom on Saturday as Middlesbrough kept alive their hopes of automatic promotion by demolishing Watford 5-1.
Kieran McKenna's team now have 80 points but are above Millwall on goal difference and have a game in hand over the south Londoners and fourth-placed Boro.
Ipswich could virtually secure an immediate Premier League return if they beat Southampton on Tuesday.
If Saints, who are also pushing for a top-two finish, win that match, the race for automatic promotion will remain a four-way shootout on the final day next weekend.
Frank Lampard's Coventry have already wrapped up the Championship title and are heading back to the Premier League after a 25-year absence.
Kim Hellberg's Middlesbrough moved to 79 points with their joint-biggest win of the season, which came courtesy of doubles from Morgan Whittaker and Tommy Conway plus a goal from David Strelec.
West Brom's goalless draw with Ipswich confirmed their Championship status for a second time in a week.
Albion were hit with a two-point deduction for breaching profitability and sustainability rules on Friday, to leave them mathematically vulnerable to relegation with two matches left.
But the point at the Hawthorns means they cannot be caught, and Oxford have been relegated along with Leicester and Sheffield Wednesday.
The teams that finish from third to sixth in the table enter the play-offs, with the winner promoted to the Premier League.