After not making any advertising buys on local, national, cable, broadcast or radio as of Thursday morning, Trump's campaign bought $1.6 million in six states -- Texas, Georgia, Tennessee, Alabama, Virginia and Arkansas -- on Thursday afternoon, according to data provided by CMAG/Kantar Media.
The biggest purchase is in Cruz's home state of Texas, where he reserved $470,000 of time.
Trump largely resisted investing in advertising until the final weeks before the Iowa caucuses, resting on his command of free media. He did eventually spend almost $10 million in the first four primary and caucus states, however.
The Trump campaign did not respond to requests for comment about its advertising plans.
Advertising is becoming more critical as the race enters a phase with multiple contests on the same date, making it impossible for candidates to invest as much in retail politics as they did in Iowa and New Hampshire. And for now, Cruz and Rubio have the upper hand, according to the data.
Rubio and his allies are spending $3.9 million this week, almost all of which is coming from his super PAC. That group has made a particularly large investment in Texas, where it has invested over $1.2 million.
Cruz super PAC ads
One of Cruz's super PACs, Keep the Promise I, on Thursday will make an advertising buy in excess of $1 million, the group's president, Kellyanne Conway, told CNN.
A competing pro-Cruz super PAC is already spending $850,000 to back him in Tennessee, Arkansas, Oklahoma and Georgia.
Those buys, combined with the Cruz campaign's $2.9 million in purchases, will send the total pro-Cruz tally as of Thursday afternoon to over $5 million this week before Super Tuesday, a date Cruz has called "the single most important day in this presidential election."
Cruz has begun a new ad in the South targeting the conservative base that replay some of Trump's older interviews, including ones in which Trump praises abortion rights and Hillary Clinton.
"Arkansas cannot trust Donald Trump," one spot in the Jonesboro, Arkansas, media market goes. "Don't give him that chance."