Francisco Sandaza's penalty was enough to give St Johnstone an efficient win over Inverness Caledonian Thistle that lifts the Perth side into fourth spot.
The Spanish striker netted his 18th goal of the season in the 41st minute after Gregory Tade fouled Liam Craig.
Tade had earlier missed the hosts' best opportunity of the first half when he fired wide from eight yards.
Billy McKay also missed chances for the hosts both sides of the goal, while a Claude Gnakpa effort clipped the bar.
The disjointed hosts had created the better chances, but it was St Johnstone who produced the more controlled display to strengthen their bid for European football by leapfrogging three points clear of Dundee United.
Sandaza scored his 18th goal of the season for St Johnstone
Saints were missing the influential Murray Davidson, who scored in Saturday's 2-1 win at home to Hearts, and he was replaced with Chris Millar.
Northern Ireland goalkeeper Jonny Tuffey continued in goal for the hosts after Ryan Esson picked up a groin injury in the warm-up at Pittodrie.
Meanwhile, Thomas Piermayr was the one to replace Josh Meekings in the Caley Thistle starting line-up following the defender's suspension after a red card picked up in Saturday's win over Aberdeen.
It was Piermayr's long ball that set up the first chance of the game and, when McKay's effort was blocked by goalkeeper Alan Mannus, Tade fired wide from eight yards as the Frenchman failed to add to Saturday's winner.
McKay was thwarted by Mannus moments later when his low shot was blocked and the goalkeeper pounced on his own spillage.
Craig headed a Dave Mackay cross a couple of yards wide at the other end.
Ross Tokely's header from a Greg Tansey free-kick was saved well by Mannus and, moments later, the visitors made Caley Thistle pay for their missed chances.
Tade barged into Craig, referee Willie Collum awarded the penalty and Sandaza scored from the spot.
St Johnstone continued to look the more dangerous after the break and a Sandaza ball across the face of goal just evaded strike partner Cillian Sheridan.
Richie Foran squandered a chance at the other end, heading over from six yards out.
Sandaza ought to have set up Sheridan for the visitors' second goal but greedily missed with his own attempt.
Inverness were looking ineffectual, yet McKay missed another excellent chance when he fired wide from inside the box.
Sandaza was denied by a finger-tip save from Tuffey, while Gnakpa's effort shaved the woodwork as neither side was able to add to the scoreline.
Inverness Caledonian Thistle manager Terry Butcher
: "We play Hibs in our next game and Pat Fenlon won't know my team because I don't know what my team will be.
"We don't have a big squad, but some of the guys who have been in cold storage will be coming out the fridge.
"You can't believe how disappointed I am. I thought we left the team that won on Saturday in Aberdeen and instead brought back 11 strangers.
"Our movement and passing were excellent against Aberdeen, but there was none of that tonight, although I felt we still had three really unbelievable chances and should have taken something from the game."
St Johnstone boss Steve Lomas
: "We rode our luck a bit early on, although the chances they had were more coming from our mistakes.
"I thought we probably could have been a bit more clinical in the second half because Inverness were pushing forward and we had opportunities to pick them off, but perhaps that is being a little bit over-critical.
"However, to come to a place like Inverness on a Wednesday night, especially after they had such a good result at the weekend against Aberdeen, and get the win says a lot about the players."
Inverness Caledonian Thistle
- 12 Tuffey
- 03 Tokely Booked
- 16 Golobart
- 19 Shinnie
- 02 Piermayr
- 04 Tudur-Jones Booked
- 08 Tansey
- 09 Foran
- 15 Tade (Ross - 74' )
- 18 Sutherland (Gnakpa - 83' )
- 21 McKay
- 43 Scott Mathieson
- 14 Proctor
- 24 Williams
- 25 Gnakpa
- 11 Ross
- 17 Morrison
- 20 Winnall
- 15 Mannus
- 02 MacKay
- 05 Wright
- 12 Maybury
- 18 McCracken
- 04 Morris (Anderson - 88' )
- 07 Millar Booked
- 09 Croft
- 10 Craig
- 11 Sheridan (Robertson - 84' )
- 21 Sandaza Booked
- 01 Enckelman
- 06 Anderson
- 16 Robertson
- 39 Gray
- 22 Oyenuga
- 24 Compton
- 46 Keatings