LIVERPOOL, England -- When is "parking the bus" actually a disciplined, well-executed plan to nullify an opposing team's biggest strength in the pursuit of a positive result? Currently, when the team is not managed by Jose Mourinho. But in fairness to the beleaguered Manchester United manager, he would have approved of the defensive performances of Liverpool and Manchester City during Sunday's 0-0 draw at Anfield.

The previously unstoppable Liverpool registered just two efforts on target, with City mustering the same. There was none of the champagne football of recent encounters, no stunning passages of play, no moments of magic from Mohamed Salah or David Silva. Yet it was an absorbing game and one that ended with both Jurgen Klopp and Pep Guardiola proving that they can organise a back four as well as a front three.

It has become something of an insult in the modern game to accuse a team of "parking the bus" when they emerge with their goal unbreached and intact. But sometimes it is simply a failure -- or reluctance -- to acknowledge the part of the game that is crucial for any team with aspirations of winning major honours.

On this occasion the two defences came out on top, but is that a bad thing? After all it cannot, and should not, always be about the forwards.

Mourinho has been roundly criticised in the past two seasons after his United team emerged from Anfield with successive 0-0 draws. But when a team plays against Liverpool, especially away from home, they simply cannot go into the game without some kind of plan to stop the likes of Salah, Roberto Firmino and Sadio Mane from wreaking havoc.

Mourinho has strangled the life out of games at Anfield more than once and been condemned for it, but Guardiola now appears to have taken a leaf out of the United manager's book by accepting that tactics need to be altered for games like these.

Last season, City conceded seven goals in two games against Liverpool at Anfield in the league and Champions League; something had to change and there was a distinct difference to the way his team approached this fixture. Guardiola deployed the pace and height of John Stones and Aymeric Laporte at centre-back: last season, the less mobile and imposing Nicolas Otamendi played in both away games and was swamped by Liverpool's front three. (Laporte also played at left-back in the 3-0 Champions League defeat and was a fish out of water on that demoralising evening.)

On Sunday, Guardiola had Kyle Walker at right-back and Benjamin Mendy on the other flank as City looked solid and well-drilled, with pace in every position. They also dropped deeper as a back four to deny Liverpool's front three the space to get in behind them and it worked a treat.

"We stood strong and showed great mental strength," said Stones after the game. "How we played was different to previous seasons. We used the ball better.

"We were so defensively solid. It was two tactical sides up against each other and it was fine margins either way, which could have won the game."

Liverpool and Man City did a fine job muffling their respective high-octane attacks in a surprising display of robust defensive football at Anfield. Simon Stacpoole/Offside/Getty Images

Guardiola also admitted after the game that it was "quite special" to keep a clean sheet at Anfield as he, once again, strayed into Mourinho territory by cherishing the shut-out.

Liverpool also played with one eye on the clean sheet, for maybe different reasons. Unlike last season, Klopp could not call on Alex Oxlade-Chamberlain to penetrate City with runs from midfield due to the former Arsenal player's long-term knee injury lay-off. His absence meant that he had to name a less offensive-minded midfield trio of James Milner, Jordan Henderson and Georginio Wijnaldum. As former Liverpool captain Graeme Souness observed after the game, all three have their qualities as team players but none of them possess the vision or flair to make a difference in an attacking sense.

Behind them, Virgil van Dijk was majestic until the moment he conceded an 85th-minute penalty -- missed by Riyad Mahrez -- following a foul on Leroy Sane.

Van Dijk's error in that incident should not mask the positives of his performance, however, or the difference he has made to Liverpool since arriving from Southampton for £75 million as the world's most expensive defender in January.

Van Dijk has become a colossus for Liverpool, leading by example from the back, and his presence has transformed the previously erratic Dejan Lovren. City struggled to beat Van Dijk on the ground or in the air, while Joe Gomez at right-back was outstanding against Raheem Sterling.

So did City and Liverpool park the bus?

It depends on your point of view, but the reality is that this was simply a day when the defenders turned up and did what they are paid to do. Both back fours bossed their area of the pitch and ensured their teams earned a valuable point, so praise them for it rather than muttering about negativity and "parking the bus."