Rotherham's hopes of staying in the Championship suffered a huge blow as they were held to a goalless draw by Luton on Tuesday.
The Millers needed a win to go into Saturday's finale at Cardiff with safety in their own hands, but will now be reliant on other results after this stalemate.
The hosts had an early effort but Kiernan Dewsbury-Hall's 25-yarder was easy for Millers keeper Jamal Blackman, while Rotherham's Lewis Wing saw his ambitious long-range free-kick saved by Simon Sluga.
Dewsbury-Hall curled wide in the 15th minute, while Ben Wiles then went close from 20 yards, his powerful effort well blocked by Town skipper Sonny Bradley.
Luton striker Elijah Adebayo saw his thunderous drive cannon off the bar with 20 minutes gone.
Town were beginning to up the tempo, with Blackman palming Dewsbury-Hall's inswinging corner against his own post.
Just before the break, United had a wonderful chance as Smith's header was met by Matt Crooks who flicked over Sluga, with the ball hitting the post and being grabbed by Town's Croatian stopper as referee David Webb signalled it had not crossed the line.
Dewsbury-Hall went close again on the stroke of half-time as Town forced a flurry of corners, volleying wide from the edge of the box.
After the break, Adebayo tried to curl in the opener just after the hour mark, but Blackman was right behind it.
United substitute Chiedozie Ogbene's first involvement was to beat two men, drilling in an angled shot that was eventually hacked clear by the Hatters' defence.
Rotherham created their best chance in the 72nd minute, Giles once again the architect, with a splendid delivery from the left that Crooks could only head narrowly wide.
Town then went close when Kal Naismith's deep free-kick was met by Matty Pearson but his header was straight at Blackman, before substitute Pelly-Ruddock Mpanzu had a great opportunity from the edge of the box, but skied well over.
Naismith tried his luck from a similar distance, as he too fired into the empty stands.
Late on, Wing's 25-yard free-kick was tipped behind by Sluga and the Hatters then broke from defence with a wonderful flowing move, but Adebayo could not apply the finishing touch, slamming over.
Town thought they had won it in stoppage time, Bradley heading home Dewsbury-Hall's corner, only to see it ruled out for an apparent push.