Kilmarnock striker Kris Boyd was again the scourge of Dundee United as his two goals dealt Ian McCall's side a blow in their battle to avoid relegation from the Bank of Scotland Premier League.

Boyd, who scored all Killie's goals in their 5-2 victory at Rugby Park in September, converted Peter Leven's 27th-minute free-kick and followed that with a clinically-taken penalty after 78 minutes to secure the points for Jim Jefferies' men.

Substitute Danny Invincibile added a magnificent third goal two minutes from time to put the seal on a professional performance from the home side.

The win, in front of a crowd of just 4,535, boosts Kilmarnock's slim hopes of catching Motherwell and securing a lucrative place in the top six before the split.

But, perhaps more significantly, it leaves United bottom of the table after Livingston picked up a point against Motherwell and in real trouble - with their next three SPL games against Celtic, Hibernian and Rangers.

McCall made wholesale changes to the side beaten by Motherwell last week, Scotland defender Paul Ritchie and youngster Garry Kenneth coming into the defence.

Captain Derek McInnes bolstered the midfield at the expense of Mark Kerr while Jim McIntyre was drafted in up front in place of Jason Scotland, who dropped to the bench alongside winger Barry Robson.

In contrast, Jefferies made just one alteration to the team which started the 1-0 defeat against Aberdeen, Invincibile being replaced by Steven Naismith in midfield.

After an opening period which at best could be described as scrappy, Kilmarnock posed the first threat on goal when Colin Nish headed Peter Leven's inswinging corner just over.

United stirred into life following that scare and a sweet volley from Stuart Duff after a corner had been half-cleared forced Graeme Smith into a smart save.

Scotland striker Stevie Crawford came into the game on the quarter-hour mark when he was sent clear by a chipped pass from Wilson.

The former Dunfermline front man dwelt on the ball too long however, enabling Freddie Dindeleux to get back and snuff out the chance.

In the 27th minute, Killie took the lead out of the blue when Boyd headed into the bottom right-hand corner for his 13th league goal of the season from a swirling Leven free-kick.

United spurned a glorious opportunity to equalise on 42 when Smith saved Wilson's penalty kick after Grant Brebner was deemed by referee John Underhill to have been brought down in the box by Leven.

Killie scrambled the ball out for a corner and from it Crawford set up McIntyre, who rolled the ball into the net - only to see the assistant referee raise his flag for offside.

At the interval Invincibile entered the fray at the expense of former Hearts and Rangers winger Allan Johnston, who had been anonymous in the first period.

McCall made his first change when Robson came on for McIntyre after 56 minutes in a move which which meant James Grady moved from the right of midfield to partner Crawford up front.

The visitors' first sniff of an equaliser in the second half came two minutes later when Archibald got on the end of a Robson free-kick at the back post to head just wide.

United were now in total control and after a sweet passing move involving Grady, Crawford and Robson, Duff blasted wastefully over from the edge of the box.

Killie remained dangerous on the break though and moments after Nish had stung Tony Bullock's hands, the striker sent Boyd through on goal but the United keeper foiled him with a fine block.

Two minutes later Naismith thundered a powerful strike at goal from inside the box which Bullock did well to beat out.

McCall played his final two cards in the 71st minute, former Ayr striker Grady being replaced by Scotland and Billy Dodds coming on for McInnes.

Killie were given the chance to make the points safe when a combined Dodds-Robson challenge saw Gary MacDonald crash to the floor and Underhill point to the spot.

Boyd smacked the ball home off the inside of the right-hand post after 78 minutes for his seventh goal against United this season, leaving the Tangerines a mountain to climb in this game and the season.

The Irvine-born striker thought he had his hat-trick two minutes later when he poked home from close range but it was ruled out for offside.

Boyd left the pitch to a standing ovation after 40 minutes, to be replaced by Craig Dargo while Gary Wales came on for Nish as Jefferies rewarded his strikers for a good day's work with an early bath.

Substitute Invincibile then added a magnificent third goal two minutes from time to put the seal on a professional performance from the home side.

Teams:

Kilmarnock Smith, Fowler, Hay, Lilley, Dindeleux, McDonald, Leven, Johnston (Invincibile 45), Naismith, Boyd (Dargo 84), Nish (Wales 84).

Subs Not Used: Bell, Fontaine, Murray, Dodds.

Goals: Boyd 27, 78 pen, Invincibile 88.

Dundee Utd Bullock, Wilson, Archibald, Kenneth, Ritchie, Brebner, McInnes (Dodds 71), Duff, Grady (Scotland 71), Crawford, McIntyre (Robson 56).

Subs Not Used: McLean, Kerr, Cameron, Samuel.

Booked: McInnes.

Att: 4,353

Ref: J Underhill (Scotland).