Paul Scholes, Patrice Evra and Cristiano Ronaldo all had the night off. Wayne Rooney turned up for just 16 minutes’ work, and the substitutions, like much of the football, were ceremonial. Not only did Sir Alex Ferguson feel able to give Gary Neville his first appearance for Manchester United in 13 months, he also felt it would be nice for old Gary to have a jog about in central midfield. When you can treat a Champions League quarter-final second leg like a pre-season friendly, you know things are going right.

Contrast United on Wednesday to the workload of Arsène Wenger’s side 24 hours earlier. “I’d love to see the stats,” said Ferguson, marvelling at the miles run by the players of Arsenal and Liverpool. Their contest at Anfield was an endurance event. When Wenger made substitutions, they were urgent and necessary. One involved replacing an injured player (Mathieu Flamini), another entailed sending on one who was not quite fit (Robin van Persie). They say nothing is more tiring than effort expended in vain, in which case leaving Merseyside in defeat must have been as draining for Arsenal as 100 unsuccessful job interviews.

It is said that all competition is a survival of the fittest. The events in midweek are not the only reason United enter today’s fixture with more vitality than their foe. Arsenal’s injury list and United’s greater squad size have meant Ferguson has been able to ration his resources at the very time Wenger, in the season’s crucial phase, has been forced to keep using his up. There could be no greater evidence of fatigue in Arsenal’s ranks than the sight of Cesc Fabregas, a Mozart of passing, hitting the ball straight to Liverpool players in last Saturday’s league game at the Emirates stadium. United’s own boy genius, Ronaldo, is not merely maintaining form but improving it, scoring in his past six games.

It is not surprising. A comparison of time spent on the pitch this season reveals that Fabregas has played 176 more minutes for his club than Ronaldo. The workload has been much lighter this season for United’s key players than Arsenal’s, and Ferguson has used rotation to striking effect. He is content to keep using his top defenders from game to game, judging the benefits of a settled back four to outweigh those that could be gained by rotating Rio Ferdinand and Wes Brown, but is determined to give his creative and penetrative players as much rest as possible over a campaign. If United’s attacking is as exuberant as it was in August, it is because Ronaldo, Carlos Tevez, Wayne Rooney and Co are fresh princes leading their army.

Rooney has played 810 minutes – approaching 14 hours – less club football than Fabregas this season and 413 minutes – nearly seven hours – less than Emmanuel Adebayor. Alexander Hleb and Flamini, Wenger’s other main attacker/midfielders, have also been on the pitch significantly more than their Old Trafford counterparts. Michael Carrick, Ryan Giggs, Anderson and Scholes have played less than Rooney, in Scholes’s case just 2,000 minutes. That is more than a full day’s less football than Fabregas. Ferguson’s treatment of Giggs and Scholes in particular demonstrates how careful he is in looking after his men. Both players had a lot of pitch time at the start of the season, but as it has worn on they have been given more respite. Scholes has played the full 90 minutes in only seven of United’s past 16 matches. He was on the bench on Wednesday, and with United gliding to victory over Roma, he did not even bother warming up.

Giggs, like Scholes, has retired from international football and is content to take it easy when he can.

“I’ve adjusted to being left out more and more,” he said. “You’ve got to. You have to realise you’re older and prepare that bit differently. I don’t get disappointed when I’m not on the team sheet, because I’m experienced enough to know I’ll play enough games, and if I’m playing well, I’ll play in the big games. Even though you want to play in every game, you’ve got to be sensible. The manager’s looking at the bigger picture and we have got a lot of players to choose from.” Giggs revealed that “sometimes when the manager doesn’t want you to play, he might give you a couple of days off and tell you not to even train but just spend a couple of days in the gym”. Still sprightly after United appearance No 751, he added: “I hope what he [Ferguson] does will help prolong my career.”

If that is a noble motive, it is also a secondary one. Ferguson’s main priority is prolonging United’s momentum and form. “I think freshness at this time of the season is important,” he said. “Arsenal have lost Flamini now and injuries are starting to eat into their season. [Abou] Diaby can’t play because he’s suspended and [Tomas] Rosicky, Denilson and Eduardo are out. We have to make sure we play with good commonsense and pick the right side. The freshness and energy of the team is terrific. Even if you look at the last 20 minutes at Middlesbrough last week, our effort was terrific. The players were up and down the pitch all the time. I’m pleased about the energy.”

Wenger was the pioneer, in England, of using sports science and data analysis to husband a squad. While Ferguson has incorporated such advances into his planning, his main guide remains that extraordinary football instinct of his. “Your eyes tell you most things,” he said. “Also, you know in a long season who you’d like to keep fresh and who you’d like to rest. For me, with the Arsenal game coming up, it was simple [against Roma]. Rooney, Ronaldo, Scholes. Put them on the bench. Keep them fresh.”

Freshness is not the only factor in a run-in. Arsenal retain such reserves of technique and willpower that it is possible for them to overcome their physical disadvantages and win at Old Trafford this afternoon. United held on to win the league last season even though they seemed to be out on their feet in some of their final games, notably the 1-0 win at Manchester City that all but secured the title. Fatigue caught up with them when they faced AC Milan in their Champions League semi-final, however, and Ferguson set out to increase his squad size in the summer, whereas Wenger – even though Arsenal suffered a similar collapse last season – did not. “Having a strong squad has certainly helped us and Chelsea this year. It didn’t last year because we didn’t have quite enough, but the addition of Carlos Tevez, Owen Hargreaves, Nani and Anderson has been fantastic for us. Those four players have made a big contribution to our season,” Ferguson said. “Tevez gave us a different way of playing. He’s such a busy little bugger and he’s scored four goals which have been among the most important goals of our season – the goal against Chelsea, the goal in the last minute against Tottenham, the goal at Liverpool and the goal at Lyons.”

It is a testament to United’s squad strength that Barcelona covet their reserve centre-back. Gerard Pique, who began his career with Barça, eased into the team against Roma. With his contract expiring next year, he admits his longer-term future is uncertain, but has no problem focusing on what is immediately before him, a meeting with Fabregas, his former youth team colleague at the Nou Camp.

United will be champions if they win their next three games, Ferguson pointed out. They have the juice to sprint for the line.

The fatigue factor: why Arsenal are feeling the strain

Arsenal have run out of energy at the crucial stage of the season, going out of three competitions in 12 weeks and victims of an 11-point swing in Manchester United’s favour in the Premier League. Because of a mounting injury list, with midfielder Mathieu Flamini their latest casualty, manager Arsène Wegner has been unable to rotate his Arsenal squad and admits key players are looking fatigued.

United, in contrast, have never gone into the domestic and European run-ins looking fresher, according to Sir Alex Ferguson. The only players he has used heavily this season have been his defenders, leaving attacking men such as Wayne Rooney and Carlos Tevez full of energy. He has been especially able to rotate in recent weeks – the very time when Wenger has had to ask the most from weary players such as Cesc Fabregas and Gael Clichy.

The contrast between the workloads of United and Arsenal players has been most stark in recent weeks. Since the fi rst ‘Grand Slam Sunday’ of the season, when Manchester United played Liverpool and Arsenal faced Chelsea on December 16, Arsenal’s creative and attacking players, such as Fabregas, have barely had a break whereas United’s have been well rested.