Few teams have done more damage to Arsenal's hopes of late than Liverpool
If an enemy's enemy is a friend, Liverpool against Arsenal can seem the friendly rivalry among the Premier League superpowers. The Merseysiders have had more-fractious relations with Chelsea, Manchester United and Manchester City. The Gunners have seen each of those three raid the Emirates Stadium for players and have a historic foe in Tottenham.
They may regard each other as the lesser of the evils. Indeed, when Liverpool beat Chelsea in the 2005 Champions League semifinals, two of the first to call Steven Gerrard and Jamie Carragher were Arsenal captain Patrick Vieira and top scorer Thierry Henry. These days, Jurgen Klopp and Arsene Wenger are likely to eschew attempts to undermine each other with supposed mind games and opt for praise and politeness. Theirs has been a mutual admiration society.
And yet when Arsenal visit Anfield on Sunday, they should not be lulled into a sense of complacency by an absence of acrimony. Arguably, Liverpool have laid bare their shortcomings more than anyone else since the start of 2014. Some of Wenger's most costly setbacks have been masterminded on Merseyside.
Their past seven league meetings have produced three Liverpool wins and a solitary Arsenal triumph, but the significance extends beyond the statistics. Four of those games have proved pivotal: Liverpool's 5-1 home win in February 2014, a 3-3 draw in January 2016 and the Reds' 4-3 and 3-1 victories last season.
The most recent had the most obvious impact. Arsenal can attribute their place in Friday's Europa League draw to their missteps against Liverpool. They finished one point behind Klopp's team. Had they even taken one point from them, they would have maintained their impeccable record of top-four finishes under Wenger.
Previous problematic days may have had greater consequences. Twice in three seasons, Arsenal arrived at Anfield top of the league. They won neither game and neither title. Liverpool arguably sent them into a downward spiral.
In 2013-14, they topped the table for 128 days, but Liverpool came far closer to becoming champions. Arsenal had only dropped two points in seven games before heading north. Starting that day, they dropped 18 in nine. They only finished seven behind eventual winners. The manner and the severity of the defeat had a psychological effect.
But 2015-16 surely represented Arsenal's best chance to win a fourth, and almost certainly final, league title under Wenger. After being pegged back by Joe Allen's 90th-minute equaliser, they did not win, or score in, their subsequent three league fixtures. History seemed to repeat itself.
Themes have recurred. Arsenal have endured defensive disasters. Their inability to mark at set pieces was highlighted when Martin Skrtel scored twice in the opening 10 minutes in 2014. Their rookie centre-back partnership of Calum Chambers and Rob Holding were exposed when Liverpool won 4-3 at the Emirates Stadium on the opening weekend last season. Negotiations to sign Shkodran Mustafi had dragged on. Laurent Koscielny was granted time off after Euro 2016. Wenger trusted the untried. Arsenal have often seemed ill-prepared for the starts of seasons; this time the narrow margins in the eventual league table indicated how harmful that was.
And Liverpool have profited from Arsenal's capacity to be slow starters in another respects. They were 4-0 up after 20 minutes in 2014, 2-0 ahead after 19 in 2016 and led after nine minutes in March. There are times when Arsenal have been floored by their pace and intensity. They have highlighted Arsenal's flaws off the ball, using speed and directness to expose a soft underbelly.
Perhaps Arsenal's lack of a high-class defensive midfielder has been apparent most often against Liverpool. Both Klopp and Brendan Rodgers have liked to use quick, inventive players in central areas, both in and behind the forward line. Arsenal have been particularly ill-equipped to halt them.
At their best -- and, as the eventual tables show, they have been less consistent than Wenger's charges -- Liverpool have looked more modern. They blew Arsenal away in an 18-minute burst that yielded four goals last August; they were 18 minutes that, nine months later, assumed a still greater importance.
In different ways, the issues involving Arsenal's Galacticos have been flagged up at Anfield. Mesut Ozil was desperately poor in the 5-1 hammering; it was a microcosm of his struggles in many a season-defining away game. Alexis Sanchez was benched for the 3-1 defeat. His frustration with his teammates had been all too evident in the previous week's 5-1 evisceration by Bayern Munich, but Wenger's stance backfired. He had to send for Sanchez as a substitute. He did not repeat the mistake of omitting the Chilean.
The sight of Anfield may induce feelings of nostalgia for Arsenal. This was the scene of their most memorable triumph, the league title Michael Thomas pilfered in the final seconds of the 1988-89 season. More recently, however, Anfield has been a graveyard for their ambitions. They may dislike some other clubs more than Liverpool, but few have done more damage of late.
Richard Jolly covers the Premier League and Champions League for ESPN FC. Twitter: @RichJolly.