Robin van Persie
Van Persie hit a hat-trick but was stretchered off late on.

Robin van Persie's hat-trick eased the pressure on manager David Moyes and secured Manchester United's passage into the Champions League quarter-final at the expense of Olympiakos at Old Trafford.

Van Persie struck twice in the first half, the opener coming from the penalty spot, before hitting a stunning free-kick six minutes after the break to help overturn the 2-0 first leg deficit alongside Ryan Giggs virtuoso performance aged 40.

David de Gea produced an inspired double save in the twilight of the first 45 minutes to prevent the Greek champions from grabbing a crucial away goal as David Fuster and Alejandro Dominguez were both denied.

Unable to recapture the intensity of their first half performance, United defended for long periods of the second half with De Gea again parrying from Dominguez but were able to keep their first home clean sheet since January to reach the last eight.

Following days of questions over his future with the Premier League champions, victory relinquishes the pressure from Moyes albeit temporarily with league matches against West Ham United and Manchester City in the coming days crucial to reclaiming the supporters' blessing.

Along with Patrice Evra's yellow card which forces him out of the first leg of the quarter final, a late injury to Van Persie who was stretchered from the field with a knee injury will be concerning to Moyes.

Reports of training ground bust-ups and the disenchantment of fans groups meant build-up to the biggest game of Moyes' United tenure had been turbulent as his side looked to better a record of seven defeats in 14 matches in 2014.

The weekend loss at home to arch-rivals Liverpool meant Moyes' position was already under heavy screwtiny and the 50 year old would risk straying closer to the exit door if United didn't oust Olympiakos and become the sixth team to overcome a first leg deficit of two or more goals in the Champions League era.

Moyes had labeled United's 2-0 defeat in Greece as the worst of his tenure and with his side's season hanging by a thread placed his trust in experience with Giggs and Rio Ferdinand both recalled after sporadic roles this term while Danny Welbeck started for the first time since January.

Despite being fresh from securing a record 41st Greek league title, Olympiakos were devoid of such riches and the continued absence of Argentine striker Javier Saviola meant illness to Michael Olaitan – who was replaced by Fuster in the only change from the first leg – was badly felt.

Manager Michel had boldly claimed his team wasn't scared of United but he had good reason to be fearful in the early moments as the home side performed with an intensity which was a far cry of their season form.

Olympiakos were fortunate not to be reduced to 10 men when Welbeck was tripped by Kostas Manolas when put clean through by Giggs before Van Persie could only toe-end Wayne Rooney's cross.

Though possessing a great verve in attack United were already leaving holes in behind and were fortunate not to fall further behind in the tie when Joel Campbell's cross was turned over the bar by Hernan Perez.

But the pressure continued from the hosts as Roberto produced a stunning save to push Rooney's header onto the post as United look destined to claim the lead.

And that advantage on the night eventually came after 26 minutes when after Jose Holebas barged Van Persie over in the box, the Dutchman stepped up to net emphatically from the resulting penalty.

Evra, captain in the absence of the injured Nemanja Vidic, almost restored parity with a glancing header which Roberto supremely turned over and Olympiakos almost took full advantage of their reprieve but De Gea saved brilliantly first from Fuster's header before an outstretched leg stopped Dominguez's follow-up effort.

The double fabulous double save would then prove priceless as United drew level in the tie in stoppage time at the end of the first half as Van Persie's side-footed home Rooney's centre.

Within six minutes of the second half the comeback was seemingly complete as Van Persie's free-kick flew into the corner, leaving Roberto motionless.

Evra's yellow card was a blot on an otherwise perfect first hour for United yet the chances continued to come for the visitors as Leandro Salino's cross found the onrushing Fuster but his strike was straight at De Gea.

United continued to sit back and Dominguez was prevented from putting Olympiakos ahead on away goals as De Gea was again equal from a tight angle.

But despite five minutes being added on following an injury to Van Persie, which could yet prove to overshadow a fine evening's work for United, Olympiakos was left frustrated to Moyes' eternal delight.