Chaplin netted in the seventh and 18th minutes, either side of an equaliser, then completed his treble early in the second half. The visitors replied but Cauley Woodrow won and scored a penalty before Bambo Diaby sealed the win late on, before a consolation goal with almost the last kick.
An astonishing match saw two spells of three goals in a ten-minute spell early in each half while both teams missed some excellent chances. But the Reds held on to claim their third win of the season and make it seven points from the last nine available at Oakwell.
The gap to safety has been cut from seven points to four while the last-placed Reds are two points adrift of second-bottom Wigan Athletic.
Gerhard Struber made one change to the side that drew 1-1 at home to Reading three days earlier, with Clarke Oduor making his first career start at left-back in place of the injured Ben Williams.
The Reds took the lead in the seventh minute when Jacob Brown embarked on an excellent run on the right wing then advanced into the box before pulling the ball back to Chaplin whose impressive right-footed finish from ten yards out placed the ball in the top right corner.
The visitors levelled within four minutes as Jordan Hugill got the better of Mads Andersen on the left of the box then had a 15-yard shot which hit the right post and the rebound was tapped into the empty net by Luke Amos.
The hosts retook the lead in the 18th minute when a corner from the right went over everyone except Chaplin who met it at a tight angle at the back post and found the top left corner with a superb powerful strike. It was almost 3-1 when another right-wing cross was turned towards his own goal by Grant Hall but goalkeeper Joe Lumley got down to his left to claw it out.
Mike Bahre was replaced by Luke Thomas on the left of the midfield diamond after 32 minutes, with Struber later saying it was tactical change as Bahre lacked 'freshness'.
The hosts felt they should have had a penalty when Brown was tackled on the right of the box by Geoff Cameron following a fine pass by Cauley Woodrow, but referee Keith Stroud did not give it. There was another appeal for a spot-kick in first half injury-time when Chaplin went down in the box but once again the veteran official was unmoved. The Reds went into the interval knowing they had been the better side against a QPR team that looked weak defensively and only had the tactic in the first half of trying to launch long balls behind the Barnsley defence.
Just like in the first half, there was a flurry of goals as three went in in eight minutes. Chaplin completed his hat-trick with a cool finish on the turn from 12 yards out after Brown’s shot from the right of the box had been saved. That made it seven goals this season for the striker and six in six under Struber.
QPR pulled one back three minutes later when Hugill got free on the left of the box and, after Radlinger blocked his effort from a tight angle, Amos again was on hand to net the rebound with a good finish into the top right corner from just inside the area.
Woodrow made it 4-2 from the penalty shot three minutes later after he was brought down in the box by Cameron. He found the bottom right corner for his ninth goal of the season.
Those goals were part of an extraordinarily open and frantic start to the second half which then saw a series of huge chances missed by both sides.
QPR nearly replied again with Bright Osayi-Samuel blazing over from 12 yards out after Bambo Diaby made a mess of a low cross from the right. At the other end, Chaplin should have scored a fourth but dragged wide from the left of the six-yard box after being played in by Thomas.
The visitors then rattled the goal frame twice within a couple of minutes before the halfway point in the second half as Eberachi Eze’s low shot from the right of the box was turned onto the post by Radlinger after a cross by substitute Nakhi Wells who then rattled the bar from the edge of the box.
The match settled down slightly until Diaby netted the fifth late on. The centre-back was up the pitch for a free-kick which Mowatt played down the right of the penalty area to Brown whose low cross was tapped in on the line by the Spaniard. Chaplin was put clean through in injury-time but saw his effort saved.
The visitors got their third right at the end of the fourth of four added minutes, as Osayi-Samuel skipped past two players on the left of the box before pulling the ball back for substitute Ilias Chair to net.
Barnsley (4-4-2 diamond): Radlinger; J Williams, Diaby, Andersen, Oduor; Dougall, Bahre (Thomas 32mins,), Mowatt, Woodrow; Chaplin, Brown. Unused: Collins, Thiam, Mottley-Henry, Marsh, Sibbick. Yellow cards: Thomas, Brown, Mowatt, Dougall. Goals: Chaplin 7, 18, 52. Woodrow 60 (pen), Diaby 82. QPR: (4-2-3-1): Lumley; Kane, Hall, Leistner, Wallace (Wells 56mins); Cameron (Chair 67), Amos; Osayi-Samuel, Eze, Manning; Hugill Unused: Barnes, Smith, Pugh, Ball, Mlakar. Yellow cards: Wells, Chair. Goals: Amos 13, 54; Chair 90+4.
-
13:43pm
-
13:47pm
-
14:01pm
-
14:02pm
-
14:07pm
-
14:07pm
-
14:09pm
-
14:13pm
-
14:17pm
-
14:19pm
-
14:21pm
-
14:23pm
-
14:27pm
-
14:30pm
-
14:30pm
-
14:33pm
-
14:33pm
-
14:36pm
-
14:39pm
-
14:48pm
-
14:49pm
-
14:51pm
-
14:53pm
-
14:56pm
-
14:57pm
-
14:59pm
-
15:02pm
-
15:04pm
-
15:04pm
-
15:05pm
-
15:06pm
-
15:07pm
-
15:09pm
-
15:10pm
-
15:10pm
-
15:10pm
-
15:13pm
-
15:15pmGOAL!
-
15:16pm
-
15:20pm
-
15:20pmGOAL!
-
15:22pm
-
15:22pm
-
15:23pm
-
15:24pm
-
15:28pm
-
15:31pm
-
15:33pm
-
15:34pm
-
15:37pm
-
15:41pm
-
15:45pm
-
15:47pm
-
15:48pm
-
15:49pm
-
16:05pm
-
16:07pm
-
16:10pm
-
16:11pm
-
16:12pmGOAL!
-
16:13pm
-
16:14pm
-
16:16pm
-
16:16pm
-
16:17pm
-
16:18pm
-
16:19pm
-
16:22pm
-
16:24pm
-
16:26pm
-
16:28pm
-
16:34pm
-
16:39pm
-
16:41pmYELLOW CARD
-
16:41pm
-
16:41pmGOAL!
-
16:43pm
-
16:44pm
-
16:45pmYELLOW CARD
-
16:49pm
-
16:50pm
-
16:54pm
-
16:55pmGOAL!
-
16:55pm