Goals from Geoff Horsfield and Martin Grainger earned Birmingham a fourth successive visit to the Division One play-offs and a two-legged meeting with Millwall.

The Blues' best crowd of the season of 29,178 had to endure a tense first half before Horsfield and Grainger struck within the space of two minutes just after the hour to seal the three points that confirmed their play-off spot, despite having Darren Purse sent off for a professional foul with 13 minutes left.

But it had not been all Birmingham's game as the Blades fought bravely for the first hour.

Former Blues player Peter Ndlovu forced the first save out of Nico Vaesen when he turned just inside the area to shoot following Rob Ullathorne's penetrating cross.

The visitors were not playing anything like a mid-table side and were doing a good job of keeping Birmingham quiet and also silencing the home fans, Shaun Murphy winning his battle with Blues striker Horsfield.

Grainger forced Simon Tracey to palm the ball away one-handed when the left-back met Stern John's cross on the volley.

Horsfield also fired wide from Paul Devlin's pass as Birmingham came more into the match.

And Tommy Mooney should have done better but shot wide from a narrow angle. Birmingham wasted their first corner when Grainger's low cross did not reach Mooney.

Darren Carter, released to play by England Under-19s, was making penetrating runs from midfield but his low cross was wasted by Horsfield's poor control.

John then raced onto a long through pass to beat Shaun Murphy and keeper Tracey to the ball but the striker's low cross was cleared by Murphy.

Vaesen got down low to his left to push Grant Smith's low left foot free-kick from 25 yards as the Blades again threatened to take the lead.

Birmingham's Bryan Hughes was the first player booked for a hard challenge on Phil Jagielka but United's Murphy was also cautioned for a lunge on Horsfield.

Tracey had to block at the feet of John as he chased Devlin's ball over the top of the defence and Devlin headed wide from a Mooney cross as the home side pushed for a goal.

Devlin sent over a cross but John headed wide as the home side continued to be frustrated in their search for a goal at the start of the second half.

Ndlovu then fired wide under challenge from Purse as he lunged to meet Smith's low cross from the left.

Birmingham's first change came when Damien Johnson replaced Devlin on the hour but within a couple of minutes the game's outlook had completely altered.

Horsfield broke the deadlock just after the hour when he prodded home from close range after Hughes had gone in bravely to win a challenge and set up the chance following a throw-on in the right.

Within two minutes Birmingham looked were course for the play-offs when Grainger curled in a left-footed free-kick from the right inside Tracey's left-hand post.

Grainger then tried his luck from 30 yards but this time his free-kick clipped the top of the cross bar with Tracey well beaten.

Grainger twice got to try from an almost identical place to his first goal but his aim was off as the ball flew over the bar on both occasions.

Purse was shown the red card by referee Phil Richards for pulling down substitute Nick Montgomery with 13 minutes to go.

But it did not matter as Birmingham's fourth successive trip to the play-offs had already been secured.

Teams

Birmingham Vaesen, Kenna, Purse, Tebily, Grainger, Devlin (Damien Johnson 59), Bryan Hughes, Carter, Mooney, Horsfield (Andrew Johnson 90), John (Vickers 78).

Subs Not Used: Bennett, Lazaridis.

Sent Off: Purse (77).

Booked: Bryan Hughes.

Goals: Horsfield 61, Grainger 63.

Sheff Utd Tracey, Doane, Murphy, Page (Cryan 75), Ullathorne, Ndlovu, Javary (Lovell 67), Jagielka, Tonge, Smith (Montgomery 72), D'Jaffo.

Subs Not Used: Nicholson, de Vogt.

Booked: Murphy, Page.

Att: 29,178

Ref: P Richards (Preston).