IT was a tale of two games last weekend for the league champions as they destroyed a Milton Keynes side in Buckinghamshire, but were unable to beat the same side 24 hours later back in Essex.
The tie was out of sight after one period on Saturday, as the Chieftains went into the first break 4-1 up, with goals coming from Darren Brown, Ross Brears and a brace from player-coach Gary Clarke.
Maxims Petruks got the consolation goal for the Thunder.
With no further goals in the second period, but plenty of action and incident, it set things up for a tense final period.
The Chieftains came out showing why they are the league champions and put the tie beyond doubt with three unanswered goals through James Ayling, Danny Hammond and Julius Sinkovic.
Former Milton Keynes man Clarke, took home the much-deserved man of the match award for a fine performance on his old stomping ground.
On to Sunday, and it was a different story altogether as the Chieftains lost at home for the first time since November, going down 3-2.
The impressive Jordan Hedley in the Thunder net, stole the show on the night with an incredible performance that was essentially the difference between the two sides.
The youngster put on a fine display and only Michael Ranby and Sinkovic were able to get the puck past the young stopper.
The former found himself getting in the showers first after a melee in front of Ryan Bainborough's net in the third period, and fists flew and the Chelmsford hard-man was dismissed.
He will miss the first leg of the semi-finals against Invicta Dynamos next weekend.
MK's goals came from Nidal Phillips and one each for the Goode brothers, Connor and Harrison.
Sinkovic was given the man of the match award after a fine play-off hockey display.
On an emotional evening, former Chieftains coach and current Thunder player-coach Simon Howard announced his retirement from the sport after a long and distinguished career that stretches all the way back to the 1988-89 season.
The Chieftains move on to face one of their old rivals Invicta Dynamos next weekend in the semi-finals of the play-offs, where one of the Raiders (either Romford or Wightlink) will meet the victors in the final over the weekend of April 20-21.
Next Games: Home: April 14 v Invicta Dynamos 18:30 (Play-off S/F second leg)
Away: April 13 at Invicta Dynamos 17:15 (Play-off S/F first leg)