World No 1 had a one percent chance by the third set which forced a dramatic collapse in Friday's men's semifinal
A US official, however, told AFP the dead included two Americans and a British national.
The Iraqi military said the rockets were fired from the back of a truck, but it did not comment on any casualties.
US Secretary of State Mike Pompeo and British Foreign Minister Dominic Raab condemned the attack in a telephone call.
The two "underscored that those responsible for the attacks must be held accountable," the US State Department said in a statement.
While there was no immediate claim of responsibility, Washington has blamed Iran-backed factions from Iraq's Hashed Al Shaabi military network, which is incorporated into the Iraqi state, for recent similar violence.
Wednesday's attack on the Taji air base was the 22nd on US installations in Iraq, including the American embassy, since late October.
One of the earlier attacks killed an Iraqi soldier and in late December, a spree of rockets killed a US contractor working at a base in northern Iraq.
That killing sent tensions spiralling.
Two days later, the US responded by bombing Kataeb Hezbollah, a faction within the Hashed that is heavily backed by Iran and which Washington has blamed for several rocket attacks.
At least 25 Kataeb Hezbollah fighters were killed and their supporters on 31 December besieged the US embassy in Baghdad.
A US drone strike outside the Baghdad airport on January 3 killed powerful Iranian military commander Qasem Soleimani and the Hashed's deputy chief Abu Mahdi Al Muhandis.
Iran then retaliated by launching a volley of missiles at the western Iraqi base of Ain Al Asad. While no personnel were killed in that attack, dozens of US soldiers suffered from brain trauma.
The tit-for-tat attacks on Iraqi soil left Baghdad furious, and in January its parliament voted to expel all foreign soldiers from Iraq in reaction to the killing of Soleimani.
Among them are some 5,200 US forces stationed across Iraq as part of the international coalition - comprised of dozens of countries - formed in 2014 to confront the Daesh group, which took swathes of territory that year.
While Daesh has lost its territory, sleeper cells remain capable of carrying out attacks.
On Sunday, two US soldiers were killed while helping Iraqi forces battle Daesh remnants north of Baghdad.
Parliament's vote on the ouster must be implemented by the government, but the current caretaker cabinet has yet to make progress on the decision.
US officials previously told AFP they considered the Hashed as a bigger threat to them than IS, given the frequency and accuracy of rocket attacks on American troops that could be traced back to the network.
World No 1 had a one percent chance by the third set which forced a dramatic collapse in Friday's men's semifinal
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