Chelsea's victory over Southampton was about power, strength and constant tactical switches – put simply, it was a rather stereotypical José Mourinho win.

Southampton dominated the opening half with their energetic, high-tempo closing down. Mauricio Pochettino's side have frequently employed a hybrid approach this season, pressing high up the pitch before dropping into two compact banks of four once their opponents play past the initial pressure, but this was the Saints at their most proactive.

Mourinho used Ramires and Michael Essien together for the first time in the Premier League, presumably because that combination was considered most likely to take the ball past the Southampton press, but Essien's early error underlined his struggles, and Chelsea were unable to attack the Southampton defence throughout the opening period. The lack of passing quality in Chelsea's back four was also obvious – the injured David Luiz can be prone to defensive lapses, but he remains by far Chelsea's best distributor from deep positions.

Interestingly, Southampton maintained their heavy pressing despite their early lead – other sides might have played more cautiously with a one-goal cushion, especially because they seemed more dangerous when they won possession in relatively deep positions, with more space to break into. While Pochettino would have been pleased with a 1-0 half-time lead, in truth Southampton's decision-making on the counter-attack was poor, and they should have created more chances. They failed to test Petr Cech following their first-minute opener and it is likely that Southampton's energetic start contributed to their second-half decline.

Mourinho made three substitutions over the course of the match, none of which was a straight swap. His first switch, on 42 minutes, was enforced because of an injury to Oscar, arguably Mourinho's key player this season. The Portuguese coach could have introduced another attacking midfielder, Willian or André Schürrle, but instead brought on Frank Lampard, with Ramires moving right. That indicated Mourinho wanted more strength in the centre of the pitch, where Chelsea were being outfought.

The interval was an opportunity for Mourinho to change his system more dramatically, however. Essien made way for Demba Ba, who played up front alongside Fernando Torres – Chelsea were now 4-4-2 with Ramires returning to a central position but given licence to charge forward. "I completely changed the way of playing," said Mourinho. "I think we gave Southampton a second half that they weren't expecting and they couldn't cope with it…the fact we played with two strikers was a problem for Southampton …we weren't afraid to press them high, and Lampard and Ramires did that very well."Crucially, Chelsea changed their overall approach to match their new formation. Their passing was more direct, with longer balls pumped towards Torres and Ba, effectively bypassing Southampton's press.

Dejan Lovren and Jose Fonte have excelled in a high line this season, but appear more vulnerable when forced into old-fashioned, penalty box defending, and Chelsea's first two goals came from set-pieces – Mourinho's side constantly put the opposition under pressure.

Pochettino responded in turn, introducing Rickie Lambert as a partner for Dani Osvaldo and moving to 4-4-2. It is debatable, however, whether this was the correct approach for a side that looked most dangerous with their slick, one-touch midfield passing – especially as no one was crossing the ball frequently, with James Ward-Prowse already removed.

Mourinho eventually replaced Torres with the holding midfielder Mikel John Obi, who sat deep protecting the defence behind Lampard and Ramires – having played 4–2–3–1 and 4–4–2, Mourinho turned to a third system, 4–3–3, to shut down the game. The lack of creativity remains a concern, but Mourinho's tactical flexibility is Chelsea's greatest strength.