Somewhere during the Staples Center celebration of Anze Kopitar’s game-tying goal in Monday’s third period, the thought occurred that the next score could decide the Blues’ conference quarterfinal series against the Los Angeles Kings.

The thought was fleeting because in the blink that it took to say “Cup Crazy” — actually 1:16 of clock time — the Kings took a 4-3 lead on Justin Williams’ downward deflection that sneaked past Blues goalie Brian Elliott.

The Kings, of course, won by that score. They won after trailing 2-0 in Game 4 to even a series in which they trailed 2-0 before returning to southern California.

It would be easy, maybe even correct, to cling to Monday’s initial reaction that the defending Stanley Cup champions return to the 314 with irreversible momentum.

Blowing leads of 2-0 and 3-2 without even reaching overtime does not speak well for a Blues team that has scored with the ease of passing kidney stones. To watch Monday’s collapse made the impression all the more unshakable.

So determined and poised in April and the majority of the first three games, the Blues reverted to their March form when confronted by the Kings’ “heavy” play.

The Blues couldn’t push the puck deep enough into the Kings’ zone to transact line changes. They got caught too far up ice on several occasions, leading to the Kings’ rapid-fire answer that produced a 2-2 tie before the first intermission.

The Kings are a load. They push, provoke and pressure. Even their playoff-proven goalie Jonathan Quick has flashed some WWE moves in the crease against smallish David Perron. All we’re missing is a chair over someone’s back.

This series has offered great theatre — four games decided by one goal, three of the games settled in the third period or overtime. To deny the Blues’ progress against a team that it had lost to eight straight games prior to the series is intellectually dishonest. Elliott has been Quick’s equal and the Blues have taken fewer of the frustration penalties that doomed them in last year’s four-game sweep in the conference semis.

But these Blues also have made the mistake of promising more.

Adding Jay Bouwmeester and Jordan Leopold offered more maturity and toughness for a back line that too often betrayed Elliott early in the season. Yet Monday’s mistakes looked more like a rightsholder’s replay from March than a No. 4 seed’s statement that it could win on hostile ice.

The Blues held their initial lead less than 10 minutes. They held their second lead a tick less than 17 minutes before the Kopitar-Williams combination landed. Outnumbered on two goals and out of place on a third, the back line gave Elliott woefully little chance on three scores. One wonders what the barrage does to the psyche of a goalie who owned April following a two-game conditioning stint in Peoria.

A team that surrendered only three goals in the series’ first 201 minutes was outscored 4-1 in Monday’s final 55 minutes. T.J. Oshie scored twice, his first two postseason goals, but thought it the worst complete game he’d remembered playing. Monday’s collapse occurred on the same ice where the Blues couldn’t protect a three-goal lead in a March 5 loss. They’ve lost seven straight games at Staples, not exactly positive reinforcement should the Kings return home for a possible Game 6 clinch.